I hate to sound rude, but this sounds like a really poor idea to me. Guinea pigs, rabbits, and chinchillas all have pretty different care needs, and none of those needs involve snuffling around in bird waste at the bottom of an aviary. I feel like you really need to do some research on each species, plus the birds you are thinking of keeping.
I'm gleaning from your post that these are outdoor aviaries? I don't know much about New Zealand's climate but keep in mind that all three species you mentioned are sensitive to heat (especially chinchillas) and temperature fluctuations (guinea pigs especially have a very narrow range of tolerated temperatures). Chinchillas are also very sensitive to humidity.
Guinea pigs, rabbits, and chinchillas are all predominantly grazers. They are best fed on a large ammount of hay plus a high quality species-specific pelletted diet. They can also have moderate ammounts of leafy greens, veg, and small ammounts of fruit depending on the species. They can't eat bird pellets, bird seed, discarded fruit/veg from birds, etc. In fact, a chinchilla that eats too much fruit is likely to get diabetes. It doesn't mean they won't try, however, and eating such foods can make them ill. Most vets say not to offer any seeds to guinea pigs as they can actually choke on the husks.
You can't mix guinea pigs and rabbits. People have, but vets and responsible keepers do not. They have different dietary needs, different gut flora (that can make one another ill), different social behaviors, etc. Plus, a well placed kick from a rabbit can kill a guinea pig with ease. You also shouldn't mix chinchillas with either species; the behaviors and needs are too different. Chinchillas and guinea pigs are both social and should be kept with conspecifics. Rabbits are slightly less social but a 'buddy' is still reccomended, however, the rabbits will need to be spayed and neutered to prevent breeding and fighting.
Finally, it seems like a really bad idea to have any of these species on the bottom of a bird cage with waste, food waste, etc. IMO it begs for an illness. We know that birds can carry bacteria harmful to humans in their waste. I don't think it's a stretch to assume that some of those bacteria, such as salmonella, could harm other mammals as well. Mixing species is just generally a bad idea for a myriad of reasons. I would personally keep rabbits, guinea pigs, or chinchillas as INDOOR pets with only their own species.
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