Honestly, I have to say that this is their loss. And in several years hopefully, they will come to their senses and realize what a mistake they have made over such a simple thing. They are choosing to shut out your LO's - it is not you choosing to shut your LO off from them. Just because they are family, it does not mean they have to be in your child's life - especially if they do not respect you and your wishes.
I live 2000 miles from all of my family and nieces and nephews (I have 5 siblings and 8 nieces/nephews). We live 800 miles from DH family (2 siblings and on niece). We don't have the option to have our families in ds's life on a daily, weekly, or even monthly basis. But, I am okay with this. We make the effort to visit at least once a year and do other things as well. But I also know that we surround DS with our friends and their children who love ds as if he were their nephew/ cousin. You and I both cannot do anything to involve our families in our children's life. Do what you can to surround your children with people who love your child no matter what you choose or how your choose to parent.