I wouldnt say issues are resolved, but I would say we have achieved a truce and fairly happy relationship, my method has been to be as honest as I can, bite my tongue a LOT and when they have got too much for me, we just havn't visited for a while.
I think over the years she has realised when she has gone too far because she doesnt see the kids for a while.
I let her do her own thing with the kids as long as it isnt causing our parenting style, problems if that makes!
She does dote on the children, and I always try and remember that she does love them a lot, I find that makes it easier to forgive.
I try NOT to rant to DH (have MN and friends for when I really need to!), but I do make him discuss issues, so we are coming at it from the same angle and if something needs to be said it is normally better coming from him.
Amazingly from where we were 10 years ago with them telling me I would ruin his life etc if I married him, I now do chat to his mum on the phone and we do sometimes have a laugh.
It can be done, but I would say it won't change overnight