My advice, honestly, is to let it go. Allow your dh's parents to have as much of a relationship as they want with your dc, let them know that you are always willing to see them, and then the ball is in their court. Some people just don't go gaga over the grandparent role. It doesn't mean they don't love your dc.
I think it gets very destructive when we try to force people to have the relationships with others that WE think they should have.
As an example: I have what most people would call a good relationship with my own mom. I speak to her on the phone a couple of times a week (and she speaks with dd), we see her around every six weeks, despite living in cities far apart, we send gifts on birthdays and call on mother's day, and so forth. During visits, we almost always have a good time. But this still isn't the relationship my mom WANTS with me or my dd. My family (me, dh, dd) is pretty independent, and we don't come to her with serious problems or ask for parenting advice, etc. She's resentful that I moved to a different city, even though we're not that far away and even though it was clearly the best choice for my family and dh's and my career. She wants her kids to be dependent on her. The result of all this is that, rather than enjoying the (really perfectly good) relationship that she DOES have with me, she is constantly disappointed that things don't live up to her fantasy--and that, in turn, takes a big toll on our relationship.
So the moral to this very long story is: enjoy what you have and find peace with it.
I think it gets very destructive when we try to force people to have the relationships with others that WE think they should have.
As an example: I have what most people would call a good relationship with my own mom. I speak to her on the phone a couple of times a week (and she speaks with dd), we see her around every six weeks, despite living in cities far apart, we send gifts on birthdays and call on mother's day, and so forth. During visits, we almost always have a good time. But this still isn't the relationship my mom WANTS with me or my dd. My family (me, dh, dd) is pretty independent, and we don't come to her with serious problems or ask for parenting advice, etc. She's resentful that I moved to a different city, even though we're not that far away and even though it was clearly the best choice for my family and dh's and my career. She wants her kids to be dependent on her. The result of all this is that, rather than enjoying the (really perfectly good) relationship that she DOES have with me, she is constantly disappointed that things don't live up to her fantasy--and that, in turn, takes a big toll on our relationship.
So the moral to this very long story is: enjoy what you have and find peace with it.