Mixed openness among kid's birth parents

My birth daughter's adoptive parents are looking to adopt again. They have another son who was also adopted. Both kids have open adoptions that include photos, updates, and regular visits. They are about the same level of openness, and we all get together fairly regularly. It's a great situation because I have a great bond with my birth daughter and her brother, and his birth parents love them both dearly. Both of us birth moms did not drink or use drugs while pregnant. We both lived a safe lifestyle and had proper nutrition, medical care, etc. We were just too young when we got pregnant to be able to care for our children. Because we have continued to make good choices, we enjoy a healthy open adoption situation. My concern is that the next child might not be able to have as open an adoption as our bio kids. What if the birth mom isn't making safe choices, or doesn't want to be in the picture at all? It doesn't seem fair to a child to have a closed adoption while his brother and sister have wide open adoptions. If this happens I would try to fill that gap for the other child. I love both my bio daughter and her brother as if they were my own. But for the other child, it wouldn't be the same. I know there's not too much I can do about it, I'm just looking for some tips on how I can best help in case this does happen.