The lack of grandparent input is one of the biggest things I lament in our adoptive experience (4 siblings about 9.5 years ago). Out of all of them, my father was the most accepting, but he was off into a lot of his own stuff, and didn't get close. My mother is a hard nut to crack anyway, and her hardness on my children is probably the same as it would have been with children we gave birth to. (Which might be the same in your case.)
My in-laws are equally distant, for various reasons. (All grandparents are divorced from each other.)
When we first announced we were going to pursue adoption, I don't think anyone in the family was for it. When we announced we were getting a sibling group, many of those suddenly tried to tell us how much better adopting a single infant would be.
Now we just plod along. We missed grandparents, but we have given our children a much better life than they would have had, and we plan on being active grandparents, if they allow that.
Brad