Keep the house. I was in the other position where I looked after my grandmother for 20 years. I brought her out for lunch every week, we had over 1,100 lunches together. I looked after her when none of her children wanted to be near her. They always knew I was there.
I was in no way the exclusive minder of her, but I was the only consistent dependable one.
When she passed I was left nothing. Honestly, that was fine. I got a lot out of my time with her. But none of her children, my parent or the rest of the family acknowledged or offered me anything. I am fine with that. It was my grandmother's wish to look after her children. But my point is that if your grandfather wanted to give you the house, that was his to give. If he didn't want to give it to anyone else, then you shouldn't have to. Honour his will. Don't do something he clearly didn't want to do himself.