This is a post-script, please pardon the double posting.
I don't know for sure what the traditional tuning is for a viola. But you may as well start there, 'cause it is harder to unlearn something than it is to learn it right the first time.
I too, frequently play in nursing homes, and it brings me a lot of joy. That reminds me that when I started, I stuck to familiar hymns and songs that I already knew so that I could be self-correcting, before I ventured farther afield.