1. In this context, I would imagine "mom crumpling" as falling to the floor; not "falling" that is accidental and results in injury. I imagine "mom" hearing the sad news and quickly kneeling on the ground as if she's too much in shock to stand.
2. In this context, "heave" means "sobbing uncontrollably". Or, you can say, crying uncontrollably.
I hope this helps :-) You're doing great <3