My condolences in the loss of your mother and sorry for all the confusing feelings you're going through. Its understandable you have these mixed /confusing feelings and agree you should speak to a counselor. Is your sister the stepfathers child? Are you in contact with her? My worry is the Stepdad might try abusing her. It must be hard feeling alienated because when a death happens, it helps to band together.

I couldn't attend my brothers service because my SIL had him cremated before we could see him. I was so upset and couldn't attend the service. Hugs to you and you're welcome to share here.