Are these pigeons the ones that were hatched here 5 years ago?

Yes they do come back because that's where they were born and maybe they want to have their kids where they were born. I'm guessing that's the children. Maybe someday when you move the eggs that there gong to hatch will have babies and there babies are going to come back to the same place. It's just a natrual thing there used to your place. Your lucky to watch them. Don't do anything to them. Let them enjoy there memos. I hope this helped and if it didn't sorry. Good luck and take care!