At only two weeks old, it can be very difficult to tell for sure. I think I would wait a bit for further plans, before I started building.
As for them being sweetest birds, if they are roosters, that also may or may not hold over with future behavior. It is so hard to believe that a darling can...
have they started crowing? Look pretty young, how sure are you they are cockerel?
Even though they are close, it is not going to be a long term memory thing, and their relationship WILL CHANGE when they grow older.
However, swapping out two chicks for these chicks might not work either. But...