You need to remember what it was like to be a daughter-in-law, not always easy, for me anyway.Also, some dil's are needy with their DH and feel overpowered by the time your son has lived with you and what I influence you exert on him.In short, they are jealous, and need to put you out of the picture a bit.In time, if you can remain pleasant and friendly with them and show that you are no threat to the marriage, then things can improve.
It's not a contest with the other Grandparents, allow them to spend money on the DGC, and you buy small quirky gifts from time to time for them, but most of all show them you love them.This is such a common thing, when a son marries, that we have nearly all had some experience of it, but unless the woman is an out and out horror, then it will get better in time.Least said , soonest mended.