I think you should leave them where they are. You say they are happy outside, your folks are happy they are outside...2 out of 3 isn't bad, and you do have your dog indoors.:lol:
I think they'd be equally happy indoors, I'd only move them in if my mum and stepdad were happy with it and I just feel I bond better with indoor animals (I'd have them all back indoors if I could)
They do come indoors but it's not the same as them living indoors - I loved waking up with Rose snuggled up on my feet when she first arrived