Ingenious concept, Nikki!!!It seems so logical what happened - as they see what they once were attracted to in the other now: a quite attractive woman. Now that they are attracted to males, it might well be that the hint of their shrunk genitalia is enough to feed this quite new need. But as mentioned, this might only be a transition period, as their need for a functional man will grow. However, I think they will never really part any more, but at least stay to be very best friends.
I think the attraction is like what you described in their story. It's safer to be with one another, to not be judge by others finding out they are not genetic females. Plus they both went through the transformation together, finding the other pretty where he doesn't see it in himself. Love it Nikki!!