I agree with your casting decision 100% but I don't know why you called Patton the victim.

Took me way too long to get that... I am not smart.

My quick guess is Paul Giamatti as the spouse slayer and probably one of the little shits from Stranger Things or whatever as the kid

Peter Dinklage is the obvious choice for the murderer.

Kathy bates is apparently interested, if we can't get her maybe Robbie Coltrane?

Ralphie May as Patton

I think if Susan Boyle gained 50 pounds and got the Charlize Theron make-up treatment from Monster she could pull it off