With my cape doves, I put the smaller chick in with another pair, or with a
pair of diamonds, for a while to get a good feed, and then return it to the
parents. But they are the sort of bird that will feed any chick. And once
they fledge, any bird they beg from will feed them. I often have several
eager cock birds waiting around trying to feed one chick.
I don't know if pigeons would do the same.
My homers generally do okay even if one is two days ahead of the other.