Terrible family issues please help?

my sister keeps stealing money from my dad and mom shes already stolen over 16k this year and we dont know if its just her or her boyfriend because he is a really big jerk and we think he could be putting her up to this. were trying to find a safer bank account because where ever bank we go she can get in because she knows all of my parents information including social security numbers and whenever she steals she always uses as it as an excuse for her little girl even tought we all know its a lie. please help