My ex is a junior on his birth certificate and he has a different middle name than his dad. His son is the 3rd on his BC and has a different middle name as well. I don't know if things have changed, the child is 14 now
No, they have to have the exact same name.
I wouldn't think so. The suffix is normally added to distinguish the name difference. My son has a different middle name from his father and is not a III.