WARNING, THIS IS GONNA GET REAL MIND SCREWY REAL FAST.

The Scarlet King, and his seven brides, have a bunch of children. The known ones are: Rosie, Holly, Junko Endoshima, Mukuro Ikusaba, 053, 999, Sayori, 682, Spike, 166, Hgan/Jack of Spades, 4547-B4, and an unknown kid from 5832. Since the brides are all sisters, this makes every one of them Rosie's cousin and sibling at the same time.

SCP-682 gets (eventually) married to Kenna, making her parent, Pangloss and Cherith, her parents in law, and Kenna's brother, Edur, her brother in law.

It doesn't end there! Since Pangloss made He Who Walks Below Dreams, that makes him her brother in law too.

This also makes the Saturn Deer her uncle in law because he's Pangloss's brother.

And because Yalbadoth is a long lost aunt of the Scarlet King, that makes Gaia and Mekhane Rosie's great uncle and great aunt respectively, alongside with Yalbadoth herself, because all together they made Adam el Asem, the first human.

This also makes Nahash, the Serpent, Rosie's great uncle too, because he is Mekhane's brother.

And because of her uncle, Dr.Clef's relationship with Lilly AKA the Violet Queen, that makes her her aunt. Also, Meri, is SCP-166, and Lilly was the embodiment of the first bride, before Clef killed her.

And SCP-4023 and SCP-6789 are also Rosie's cousins because Mekhane and Yalbadoth made them.

SCP-3000, aka Anantashesha is also Rosie's great uncle because he's also the brother of Nahash.

SO YEAH, THAT'S ROSIE'S FAMILY TREE.