I hope you are keeping a journal on anything they may be repeating. Don’t ask for details, just write don’t what they say. Parental Alienation is a common tactic, and you have to be ready for it.
Unfortunately, it is very easy for a mother to do this to the children. There is a bonding between children and their mother that exceeds understanding. That is why children are much less likely to report abusive mothers, then are are for fathers. Even if the abusive is so severe as to be fatal.
I had a call, just an hour ago, from the mother of my home aid, Kimberly. Kimberly’s children have lived most of the life with their grandparents, but yet Kimberly has got them convince that they are unloving and uncaring.
And she only sees them once a week. I know these people, and I know better. But, it shows how easy it is for mothers to manipulate their children. and that is something you need to be watchful for. I have seen hundreds of such cases over the last decade.