Lisa , no knowledge of gouldians breeding but silverbills yes .
When i first acquired some silverbills I purchased 5 , supposed to be 2 pairs and a spair bird unknown sex .
From that original 5 birds I now have 3 and one hen that they bred .
From my experience with zebras and societies sharing a flight I could not recommend this . Too much disruption with birds vying for dominance and those pilfering zebras taking from everyone .
Headwrecking .
Currently I have 2 breeding pairs of silverbills and very different they are in their breeding needs .
1st pair are free breeding and are currently on their 3rd clutch , fledged about 1 week now , 4 chicks and really going well . this pair have laid eggs in the feeders and on the cage floor before i supplied nest boxes to them , ( half open fronted and wicker )

2nd pair are very nervous breeders and are only now rearing their own chicks after third attempt this year .

Put them in quiet corner of birdroom and just left them alone .
Hope this is'nt too long winded and you get some help from my experience .
Regards , Mick M.
1st clutch fostered under societies , 1 survived to fledge .
2nd clutch under societies fledged 3 and all 4 doing well in flight cage.
3rd clutch of 5 , last one fledged today and all looking fine and fit., Im delighted with results .
Between the 2 pairs I now have 23 offspring , if they all survive .
They did all take egg food sparingly and all chicks look in excellent health .
The one thing i can take from my observations is that my silverbills when accliamitised to my set up just wanted to be left alone to get on with living and breeding , fed and watered they will more than repay their keep .
I breed all my finches in box type cages (24 /16/16inch)with no interference from others and i find it works best for me .
Hope this is some help to you , might not answer your questions directly . Zebras and bengalese cant be trusted not to interfere . Whatever you decide I hope it works for you .
Regards , Mick M.