I come from a vast, sprawling family of relatives with widely disparate ages and not everyone is a "full" blood relative to everyone else. In my family, it doesn't matter if you share a father with the babies. They are still your siblings and should be treated as such. If you have a more or less familiar relationship with them due to age, whatever, but they're family.

I mostly wonder, from the twins' perspective, how hurt they're going to feel when their older brother doesn't want much to do with them. I don't feel bad for the LW. I do feel bad for the kids, because I have yet to meet children who don't take familial rejection very, very personally. Hopefully the soon-to-be-middle child will help make up for the bad feelings.