Hi Roger,
Generally it is not a good idea to try to breed birds in a colony – especially peach faced lovebirds as they can be very aggressive. I hope you have a large walk in aviary? If this is just a large cage, you need to re-think your set up. Female lovebirds can be extremely territorial and aggressive and it’s probably just a matter of time before you have serious fighting. It is never a good idea to have an odd bird out. Again this can result in fighting. It sounds like the odd bird is more likely a male. But even if it was a female, neither of the paired males would try to mate with it. Lovebirds will only have one mate at a time and generally only get a new mate if something happens to the old mate.
I would recommend one pair of birds per cage. Even if you have an aviary, there is a high chance that they will fight. Females have been known to raid a rival’s nest, destroy the eggs or kill the chicks. Once any chicks fledge from the nest box, they are in danger of being attacked by one of the females. All you can do now is see how things play out since they are already sitting on eggs. But watch them carefully and if they do hatch chicks, either hand feed them after a couple weeks or be sure to remove them from the cage as soon as they can eat on their own. I hope everything goes well, but if it does, it will definitely be the exception.
Thank you for asking Lafeber,
Brenda