Adult and married step children what would you do?

My husband and I have been married for 15 years. All grandchildren have been born after our marriage and know us as grandparents. I have 4 biological children that love and respect my husband and is allowed access to the 7 of them from day 1. They spend time with us because we are good to them and love them and my children trust us to protect them with the best of care. My step son and step daughter in law home school their 3 children ages 12, 9, and 5. The step daughter in law does not allow us any alone time with these 3 children because she does not want her children to ociate with my grandchildren because they are in public schools. The daughter in law tells us what we can and cannot buy for her children for christmas and birthdays and once informed us that if we purchase to much for her children they will not spend another Christmas with us ever again. This daughter in law is very rude and hurtful and expects us to visit quite often and it is a 110 mile round trip to do so or else we will be cut off from them. My husband works 7 days a week and preparing for retirement in a couple of years. All holidays are separate from my children although everyone of them have welcomed her and are kind to her. She allows the children to call their grandfather pa and I am called by my first name. Their real grandmother lives 1,000 miles away and does not visit them in person very often. The daughter in law is not happy with the real grandmother and does not have much to do with her and she is always bickering with her own mom and step dad. The step son over the years has become as bad as she is and my husband bends over backwards to please them and never stands up to them when they are disrespectful toward me. My husband and I have never had any issuess with each other in our marriage unless it had to do with his kids. Anyone have any advice because I am wearing out here?