Hi,
If you want to keep a colony of finches, you cannot allow breeding. You should never provide nests of any kind, and if any bird tries to use a food bowl as a nest, you need to remove the dish and replace it with something too small to sit in. It sounds like your society finches bred and then you added the two odd birds. Generally weaned chicks should never be left in the same cage with the parents. Their instinct is to drive the chicks away and this is nature’s way of preventing inbreeding. In captivity, sometimes instead of chasing the chicks away, the parents start mating with the chicks. You should never allow related birds to breed. When keeping a mixed colony of birds, you must be OK with throwing away any eggs that are laid. If you have a problem doing this, then don’t keep all of these birds together. If any eggs are laid, it will likely result in fighting. You may end up with dead birds, or the eggs will get destroyed by any females who didn’t lay eggs. So again, a mixed colony can work out as long as you keep it non-breeding. The cage needs to be large enough, also.
Now to address that you have an odd number of birds as well as related birds. One suggestion is to find homes for the chicks, and then get another Zebra finch and another Gouldian. That way everyone has a companion and nobody is left out. As it is now, the zebra and Gouldian are odd birds, and in this mix, there is a chance that 2 of the society chicks will form a bond, one will bond with the zebra or Gouldian, and now you have an odd bird out that is likely to be bullied by the paired birds. You can get a same sex zebra and same sex Gouldian and they are likely to take up with their own species in spite of being same sex. The most important points here are no breeding, not keeping related birds together, and keeping the numbers even. This makes the colony more likely to remain compatible.
Thank you for asking Lafeber,
Brenda