I wouldn't, even though they come from the same region of Madasgar, I doubt they actually spend significant time together, different species are susceptible to different diseases, and you should never mix them together.
No, because you shouldn't have a Ploughshare at all.
Why take a critically endangered animal that has already been torn from its natural habitat, contributing to the decline of the species and put it at further risk by cohabiting it with another species? Why give the poachers incentive to remove more of them from the wild in the first place?
I agree 110% with Kristina. A species that is severely plighting in the wild doesn't need someone who's 'interested' to add on to the burden. Ploughshares should not be kept by people, save the turtle conservatists in Madagascar who are desperately trying to save the species.