Well moved my dad into my sisters place

What a day it was busy and a lot of work and very stressful. My dad has alzheimers and he is not doing to bad pretty good considering. He handled the move pretty good. We got him settled in and I found out from my mum not only did my dad pay for the renovation to my sisters basement he is also going to pay rent while he lives there. I don't know what to think of all of this maybe I'm crazy for being upset but I think she is taking advantage of him in his confused state. I guess I should just let it go but I think it's wrong. Correct me if I am.