I also had fraternal twin boys. Fraternals so not have to look alike and can be different sexes. However, as in my case, the likelihood of having twins increases as a woman ages. However, fraternal twins do run in families, but only on the mother’s side so Carrie being Roman’s daughter has no bearing.
Kate’s twins don’t count, as they were implanted and this often results in multiples.
Anyone can have identical twins (Marlena) cause it is just a single cell spliting –they are always the same sex and look alike.