Wanda: I think our family trees must be the most convoluted in history, Vision!
Scarlet Witch and Vision's marriage. Vision is a robot built by another, evil robot Ultron, who was himself built by Henry Pym. Ultron has an Oedipus complex with both Pym and The Wasp, considering them both his "parents", and bent on killing them.
The Vision was built using Wonder Man's brain patterns — in spite of Wonder Man being dead. When Wonder Man came Back from the Dead, much like Vision, he had a crush on Wanda. Wonder Man's brother, the Grim Reapernote NOT the literal one, which would make this even weirder also considers the Vision his "brother". The Vision was also built (or not) using the body of the World War II-era Human Torch, which is a Continuity Snarl of its own.
Scarlet Witch's twin brother, Quicksilver, was formerly married to Crystal of The Inhumans, and together had a daughter, Luna Maximoff. Crystal is currently married to Ronan the Accuser. She is also the sister of Medusa, Queen of the Inhumans, whose husband Black Bolt is the king and head of the Inhumans Royal Family.
Wanda is formerly-but-still-possibly the daughter of Magneto. Besides the Maximoff twins, Magneto also is the long-lost father of Polaris. Had Polaris not been forsaken at the altar, she would have married Havok, one of the Summers brothers, and tied together the two biggest and most snarled family trees in Marvel.
Polaris might have a half-sister Zaladane but she's dead.
The Vision and Scarlet Witch have two sons, thanks to magic. They were both erased from existence but then reincarnated into Wiccan and Speed of the Young Avengers — a team with a different Vision, rebuilt from the original's brain patterns by Iron Lad, a younger persona of the time-traveler Kang the Conqueror. This led to a love triangle between Stature, Iron Lad, and the Vision with Iron Lad's brain patterns.
Through Kang is a link back to the Summers family — he's a descendant of Doctor Doom and Nathaniel Richards (the latter of whom is Mr. Fantastic's dad, and great-grandfather of Hyperstorm). This also throws in Nathaniel's family (including his other children), Kang and Immortus's litany of sons named Marcus, and Kang's lady friend Ravonna who posed as Nebula for a while.
Wiccan is married to his teammate Hulkling, who is the son of Mar-Vell (the original Captain Marvel) and the Skrull princess Anelle.
After Mar-Vell's death, his lover Elysius used his genetic material to artificially conceive a son Genis-Vell, who was forcibly aged to adulthood. Genis-Vell, with his vast cosmic powers, did a Universal Retcon — and in doing so retroactively created his own sister Phyla-Vell. Then Phyla wound up with the Guardians of the Galaxy and in a romantic relationship with Moondragon, the daughter of Mar-Vell's old ally Drax the Destroyer.
The Vision also built himself a robotic family: Virginia, his wife, who was constructed with the Scarlet Witch's brain patterns, Vin, his son, and Viv, his daughter.
Ultron didn't stop with the Vision: he created Jocasta (with Wasp's brain patterns), Alkhema (from Mockingbird's brain patterns), and Victor Mancha (who joined the Runaways). In keeping with the Oedipal theme, Pym had a relationship with Jocasta after the Wasp died, and Alkhema has a "daughter" named Antigone.
As of Avengers Academy, the abomination that is the Pym family tree has another new branch in William Grant Nelson, the son of Tigra, who is Hank's biological son via a Skrull infiltrator who had perfectly replicated Hank down to the DNA. From a certain point of view, this makes him Ultron's half-brother. A fancomic poking fun at William's family tree shows Wiccan playing with baby William. Hulkling asks how they're related and after doing some math, Wiccan concludes that the toddler is his great-uncle.
In an alternate universe, Scarlet Witch has a daughter Nocturne with the X-Men's Nightcrawler. Since Nocturne lives in the main universe, by Marvel standards she would be included in Wanda's family tree (see: Summers family tree). This attaches Nightcrawler's mother, Mystique, Mystique's deceased wife Destiny, and their adoptive daughter Rogue, and Mystique's current husband Charles Xavier into the tree as well as a few other notable characters.
In Marvel Comics, the Olympian gods are just as twisted as their Mythological counter-parts, if not more so: The Elder Goddess Gaia is the sole "earth-mother goddess" of all of Earth's pantheons. She achieved this by, in different guises, mating with each pantheon's father god — even those who were her own descendants. This means that all of the different gods of different pantheons are related to each other through her; Thor is Zeus's uncle (and grand-uncle).
The second Ghost Rider Danny Ketch and his late sister Barbara turned out to be Separated at Birth siblings of the first one (if you don't count a Wild West character later renamed Phantom Rider), Johnny Blaze, and the spirit who inhabited Ketch's body, Noble Kale, is their ancestor by mother.
In Iron Man Ezekiel Stane is the son of Obadiah Stane, aka Iron Monger. Sasha Hammer is the granddaughter of Justin Hammer, and the daughter of Justine Hammer and the Mandarin. Ezekiel and Sasha are dating. If they ever have a kid, said kid will be related to all of Tony's archenemies.
poking fun at William's family tree shows Wiccan playing with baby William. Hulkling asks how they're related and after doing some math, Wiccan concludes that the toddler is his great-uncle.