ROMANOV / (BLACK WIDOW) FAMILY TREE
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Tzarina?
The Black Widow was an infant in 1928, recovered from the rubble of a collapsing building in Stalingrad (now Volgograd) by a soviet soldier Ivan Petrovich Bezukhov. This places her birth either 1927-1928. The woman whose care she was under (possibly her mother) was crushed by the debris. However, before she died, she claimed that “Natalia” was a “Romanoff, but..” [Black Widow: Deadly Origin #1] (When translated from Russian, her name can be read as "Natasha Romanoff" or "Natalia Romanov", or Romanova for the feminine version.)
The Romanovs were the Russian royal family that ruled from 1613 to 1917. In real world terms, the ruling branch of the family were all killed during the communist revolution. However, fate diverged in the Marvel Universe. Princess Anastasia was saved from the massacre by a young communist deserter who had fallen for her named Ivan Korovsky. Faking her death, the couple fled, eloping in the Siberian city of Tomsk. For several months, Anastasia was protected by her new husband and loyalist soldiers but they were eventually discovered by the communists and Ivan and many of Anastasia's protectors were killed. Anastasia alone managed to escape to the countryside.
Sometime later, she awoke up in a hospital in Berlin, confused as to how she had gotten there. She proclaimed that she needed to return home to Russia to ascend to the throne but she was not believed by her doctor. In Strange Tales (1st series) #24, Anastasia seemed to think her family had been cursed by Grigori Rasputin (for more on Rasputin see the Rasputin Family tree). In the conclusion of the story, Anastasia lost consciousness and was haunted by the vision of Rasputin. If Anastasia did survive and escape the hospital in Berlin, by 1928 she would have been 27 years of age and an appropriate age to give birth to Natasha.
While this may seem like an outlandish idea, stranger things have certainly happened in the Marvel Universe. There is also some contextual evidence supporting this theory. Natasha remained in the care of Ivan for her childhood years but was later given into the care of master spy and alleged kinsman, Taras Romanoff. Romanoff trained Natasha for several years, the pair masquerading as father and daughter before he was assassinated by the future X-Man Wolverine. [Wolverine: Origins #9] After Taras' death Natasha returned to the care of Ivan, only to be targeted by Nazi super-villain Baron Strucker and the Hand. 
Their intention was to brainwash Natasha and turn her into an assassin. The villains said they picked her specifically because they thought dispatching Natasha against their communist enemies was poetic justice for the Bolsheviks’ own slaughter of Natasha's imperial kin. As other (albeit more distantly related) Romanovs such as Taras existed, it would appear that Natasha own ties to the Romanovs must have been stronger for her to be the one chosen. An explanation could be that she was Anastasia's daughter, as this would explain the increased interest in Natasha (who is essentially an orphan) and also explain “Romanoff but…” if she were descended through the female line. Ultimately, how exactly Natasha fits into the royal family (if at all) remains a mystery and this theory could well be disproved. [Uncanny X-Men (1st series) #268]
The Black Widow's Mates
After the thwarted kidnapping attempt by the Nazis, Natasha (despite her age and sex) defended her nation in the armed forces during World War II. She met her first husband Nikolai while they fought in the same military unit. Despite Natasha being only sixteen and Nikolai seventeen, they opted to marry informally. Nikolai's wedding ring to Natasha was a piece of silk that he tied around her finger. This was a very personal gesture, as Nikolai's mother had sewn this fabric into his uniform so she could stay close to his heart when he was in battle.
The young couple's brief but significant union resulted in a pregnancy but things were not meant to be. Nikolai died shortly thereafter, killed in combat and Natasha's delivered their baby girl, “Rose,” stillborn. At this point in her history, Natasha had been exposed to the Soviet version of the super-soldier serum, created by Dr. Lyudmila Antonovna Kudrin. The serum, while granting her longevity, treated pregnancies as an infection and removed Natasha's ability to carry a healthy baby to term. From time to time as she grew older, Natasha would think fondly of Nikolai and what might have been had he and their baby survived. [Black Widow (4th series) #4]
[Note: This is a substantial contradiction in Natasha's history as, according to Black Widow: Deadly Origin, Natasha was in her late twenties not a teenager when she (along with Ivan) received the super-soldier serum.]
Despite the loss of Nikolai and Rose, Natasha did eventually remarry. The actual legitimacy of this union is somewhat in question, as in some accounts the marriage was a total sham designed as a cover for two leading Soviet agents. Natasha's own memories of her past are also distorted, so the truth remains unclear. Alexei was a test pilot for the Soviet government. His death was faked in 1963 by then leader of the USSR, Nikita Khrushchev, as he became the Soviet “super-hero,” Red Guardian all unbeknownst to Natasha. Privately, Alexei confided in Khrushchev his belief that Natasha's inability to have a child was a factor in the failure of their marriage, as it tormented her and made her difficult to live with. Regardless, Natasha took Alexei's death poorly and blamed the United States. She became an antagonist to the West before eventually defecting and become an integral part of Avengers. [Black Widow: Deadly Origin #1-4] Over the years, Alexei has resurfaced following and has been both enemy and friend to Natasha but never again husband.
Following Natasha's defection to the West, her father figure Ivan developed an unhealthy interest in her. While the serum caused gaps in Natasha's memories, it appeared to rot Ivan's mind all together. Ivan made his romantic intentions clear to Natasha but she was not open to them, as her interest and need for him in a familial role was paramount for her. As the serum continued to degrade his mind, he started to plot against her. Destroying his own body, he had his brain transferred into a mechanical form and took control of a Russian space station with nuclear warheads hoping to force Natasha to be with him. Natasha managed to kill him before he could cause any damage. Natasha mourned Ivan, feeling that the monster she had defeated had actually killed her “father.” [Black Widow: Deadly Origin #1-4]
Natasha's ultimate wish for family was finally fulfilled in unsurprisingly a very peculiar way. Several of Natasha's enemies decided on a novel approach to get rid of her by giving her a dream life. Selecting a seemingly perfect “fiancé” named “James,” the coterie of villains mind-wiped both Natasha and “James” and artificially grew a one-year old son named “Stevie” from their DNA. A veritable ringer for his mother, little Stevie also inherited her natural escapist skills, with Natasha referring to him as a little “Houdini.” The new family was placed in San Francisco where Natasha was given an identity as a high-powered architect “Natalie Grey.” This idyllic new life only lasted three months, as Natasha's old one came back with a vengeance when she was attacked by an old enemy named Weeping Lion. The assault from Weeping Lion triggered the return of her memories. Seeing no choice, Natasha faked James and Stevie's deaths in an effort to protect them. Father and son currently reside in a safe house on the northwestern coast of America. Natasha specifically requested the location be hidden from her, as she thought it was in her family's best interest. Who James was prior to his abduction or what his real name was never revealed. [Black Widow (8th series) #1-5]
In one alternate timeline, Natasha had a child with the American “super- soldier,” Captain America. Possibly the Captain's own exposure to the United States super soldier serum counteracted Natasha's own serum's resistance to pregnancies, allowing her to carry a child to full term. Very little is known of her son's history, save that he was one of a number of second generation superhero teens in the care of a future version of the Hulk (Maestro) following their world's collapse at the hands of Ultron. The boy, James Rogers, was in possession of a version of his father's shield and operated as the de- facto leader of these teens. [Avengers (4th series) #1-6] Eventually, he and his peers managed to journey to the past and entered the service of on-again and off-again S.H.I.E.L.D. director, Maria Hill. He has not reappeared. [Avengers World #9-11, 14]
Other Spiders?
Natasha was one of a number of Avengers that were cloned by a Deadpool villain named Dr. Bong. He was using the clones to steal weapons but later killed them himself when they outlived their usefulness. [Deadpool (4th series) #27-28]
Natasha also allegedly has two brothers, however neither make much sense in Marvel canon. The first such brother, Vindiktor, appeared in Shadows and Light #1 as an antagonist during one of Natasha's returns to Mother Russia. Horrifically burned, he claimed to have been in the same fire as Natasha as a baby and that he was only one of several brothers that Natasha had. This was his only appearance and he died with his relationship to Natasha being unproven and highly unlikely, given any true brother of Natasha would be quite elderly. As this was a short story with a prestige format (black and white illustration art style), it seems unlikely that this story was intended to be canon and was effectively a "one-off". Despite this, Vindiktor has been referenced on and off again in some handbook entries for Natasha, which is why he is mentioned in this article.
Another brother of Natasha, Alexei Romanov debuted in the young adult book novel Black Widow: Forever Red. He was allegedly born around the fall of the Soviet Union (1991), so again he does not fit for Natasha's personal timeline. It was unclear if he was intended to be a full-blooded sibling or a half sibling. Alexei was also a romantic partner of a protege of Natasha's named the Red Widow, another graduate of the Red Room. As a young S.H.I.E.L.D. cadet, he took part in a mission with his sister and girlfriend but died tragically in the field. Usually, novelization characters would be dismissed entirely from articles such as this, however Alexei's status is complicated by the fact that he went to appear in two back stories for Mockingbird: S.H.I.E.L.D. 50th Anniversary #1 and Ms. Marvel (4th series) #12. Unlike Vindiktor's debut, the artwork for the story was a traditional comic book art style. The most likely scenario is that these back-ups were intended as promotional materials for the novel series but this was never expressly stipulated. Saving information to the contrary, it seems appropriate to include Alexei in the chart as a “possibility.” If he is indeed “canon” upon his death, he was survived by a foster mother, also a S.H.I.E.L.D. agent named Marilyn Manor.