Except for the ball rolling around the sheet. I think it would be faster and most likely better to make it work using morphs and animate them when needed.

(2.) Might be possible with bullet physics, haven't played that much around with it my self, but I recall a tutorial showing that you could make some jelly effect, so that might work. Using dynamics is also possible, but that would require that the objects you use are modeled with some sort of internal structure as Poser dynamic room doesn't have a balloon effect. I made something similar for my dynamic bed so should be possible for a cushion and mattress as well. And done correctly I think it could work quite well actually.