Well yeah, that's one possibility. It'd explain why the twins are older than their cousin. (I forget Quicksilver's daughter's name at the moment.) In this scenario, they still have demon souls, and Mephisto may come after them.
Another possibility is that the twins are real, and Wanda gave them up for adoption. She then repressed the memory and created the false twins out of guilt.
Hopefully if we get YA season 2 they'll explain it.