A smart plan would be to talk to the probation officer, tell him your suspicions as well when it comes to the theft of the pain pills, as she is probably selling them. As for your step-daughter, shes made her bed, let her sleep in it. Tough Love Brother.
As for her Mother... if she had been a better parent, maybe the family wouldnt be going thru this grief as well. She needs to either step up as a parent and cut her apron strings, or move out with her and find out exactly how bad it can get down that rabbit hole. Either way, COVER YOUR ASS. Money, savings, valulables, ect ect. You are a smart man, and you know the deal, make sure you got yourself covered.