J.M.
I think you have gotten some great advice! Unfortunately that is a very common scenerio with blended families. My mother/family has taken in my step daughter as a member of the family...I still catch my MIL playing favorites a bit which she claims is because of age. My step daughter is 10 and my daughter is 4. My FIL doesn't consider my daughter one of his grandchildren at all (they are divorced, so it's 2 halves of my DH's family). We hope that once we have a baby together both sides of the family will be more accepting of us as a family unit.