It makes sense to me too. That really is a lot to deal with. I don't like change, and as much as I always moved around, I associated certain places with stability, and I don't like those places to change (like my grandparents' houses). And I bet it feels wierd that your sister is buying your parents' house too, and maybe you are questioning where your place in the world is. I can understand having stress about all of that.
((((((((((((hugs))))))))))))))