No project would get solid results with only two individuals, correct, as it would be a flawed sample size to begin with, but it at least would have some possibility of results at all. I simply don't get what the results of your proposed project are supposed to be? I guess based on the guidelines of the project, just a vivarium that fits the generally accepted guidelines of care for the two species and has two animals in it. I may simply be failing to see it, but the only proposed benefit of adding the actual animals is for audience appeal. That fails one of the basic questions of ethical animal research, which is "why are animals needed?" You may well never get called out on that, but I'd consider it if I were you. Particularly if you ever might want to discuss the project as support for being accepted to work in an animal research lab in university or beyond.
