Is your daughter a minor? If she is a minor, and their behavior continues or intensifies, you might seek legal advice regarding this issue.
It is usually possible to amend your Judgment with a clause stating that nobody shall make, or cause others to make, any disparaging remarks about either parent in the child's presence or within the child's hearing.
If she is not a minor, then there is not much you can do other than to try to let their words roll off your shoulders and let your behavior and words show your daughter how wrong her grandparents are.
I'm so sorry you have to go through this. Good luck to you all.
