The limit is 1. The only time you really need a letter form your shrink (can't be from your MD) is to bring the animal into the cabin of a plane, or to bring one into public housing. You can only bring one.
Emotional Support Animals are not covered under the ADA. Prescription means nothing. A doctor won't write a scrip for more than one.
Would that work for what? You've already been told numerous times that ESA animals are not protected under ADA laws and can be denied by a landlord.