I could sit here all night telling stories about what tenants do to rental property. With that said (or unsaid, as I don't have the time), I think you are right to continue looking for a better situation for your parents. Good luck in your search!
I agree, and I also sympathize with landlords who just want to make a living, build some investment/retirement and do the right thing by their tenants, but get incessantly screwed by scumbags. I've had good landlords and bad landlords in my life. The good ones really make your life easier, the bad ones really stress you out.
I'm glad to be a homeowner, but it really sucks to have to go through this rental hunt again and have to co-sign on a lease for my folks, but it is what it is, and it do what it do. It should just be temporary, but finding the right place is much more stressful to me than co-signing for them.