Step Daughter problems (need advise)

I forgot to mention that I have been down the stepdaughter road before, so I feel for ya. As well my oldest son moved out to his moms after me raising him for 17 years. He was skipping school (got kicked out) found pot and stole money from me. He is only 3 credits away from his diploma. Mom is a waste of saggy foul flesh cuz she had nothing to do with them all this time, now allows him to do nothing.