What strikes me on this thread is the focus on being a mil in terms of gc, parenting etc. Imo this is the whole problem, because that isn't about being a mil, that's about being a grandparent.
Being a mil is the relationship between you and your daughter/son in law, separate from your future gc. More specifically Dil as this is often where tensions are found.
The focus should be "I hope to be friends with my Dil", "I hope to build a genuine bond with my Dil", and Visa versa of course, not I will do this and I will do that for gc.
In my opinion, and in my experience as a Dil, it is almost as if this is simply a title with little meaning, only that she is the route to you becoming a grandparent. It's really sad, and it why mil/Dil are so strained. They aren't real relationships. Not in most cases.
Those that get on with their mil do so because they have a friendship built before gc, and away from gc's. A friendship between 2 individuals, like any normal friendship that is worked on over time.
When introduced to a new partners parents, a Dil is always the outside to start with amongst a new family. If she is embraced by mil then a friendship can begin to form. What tends to happen however is as the mil is in the position of power, she maintains this, usually up until the point that gc are born. Once the dynamic shifts, and a separate family is formed, if no friendship has formed it's pretty much a one was street in terms of the Outlook for mil/Dil future relationship.
I hope to remember to be Dil friend. That's my focus.