Hi Lydia,
Nests are really not needed for birds unless they are breeding. In the wild, with very few exceptions, birds do not use nests year round. Nests are only used during breeding season and then they are abandoned. Birds do like to feel safe when they sleep at night, and will generally choose a high perch. It’s possible that your flight cage feels too exposed, so they feel safer in a nest. But nests trigger breeder behavior, and that results in territorial fighting. Replacing the eggs with fake eggs only means you do not have offspring to deal with. But if your hen keeps laying eggs year round, she will eventually die from the strain of laying too many eggs. In the wild, she would only lay eggs once or twice in the breeding season, once per year. You might try placing some perches up high in the flight, and covering part of the flight where they feel like they have some protection at night. They would normally roost in a tree and have branches and leaves for cover.
As to the fighting, the young male may have wanted to still be fed. He’s not likely to be mature yet, but you really never know with captive bred birds. They do reach sexual maturity at a much younger age than in the wild. A little bit of chasing and fussing at each other is OK, but if it is constant, or if feathers are being pulled or blood is drawn, they need to be split up. Grown offspring should never be left to live with the parents. It either results in fighting or inbreeding. If you keep all of these males, not only will the fighting keep going, but they will all end up mating with the mother. It’s not a good balance, and adding females is not a good idea, either, since you have related birds in the cage. I would find homes for the young males, and let the parents have their flight back. But you still don’t want to give them the nests. The female is just going to keep laying eggs as long as she has a nest to lay them in. She might still lay some without a nest, but if you do your best to keep her from making a cup or corner of the flight into a nesting place, she will most likely give up. Birds need a safe place for their eggs, and if you change things around and prevent her from nesting anywhere, she won’t be as likely to lay eggs or at least not as often.
Finches do enjoy the small colorful plastic toys that are made for small birds. They will peck at bells, colorful beads and enjoy swings and the “Olympic” ring toys. This kind of thing can give Leo and his wife something to do other than mate! LOL I really think your pair would be happiest if their youngsters were not with them. I’m sure their instincts are telling them to send the boys packing, but they can’t do anything about it.
Thank you for asking Lafeber,
Brenda