should I just zip it till after Christmas?

Hey everyone.. I think I'm in need of some advice.

I'm fully out now, and I've just changed my pronouns to neutral ones (they/them) My SO has been more then supportive with the change. However, I'll be spending Christmas with his family and I'm a little worried about how the pronoun change will turn it into an uncomfortable time.

I've talked with my SO about my concerns, asked him to explain it to his mum and perhaps she can inform her partner sorta thing. He said he is willing to, though he can't guarantee they will agree with it. I've expressed my understanding, that not everyone know's a non binary person and has never faced a pronoun change.. but he seemed to keep bring up the negative. Like he is certain they won't agree to this.

I guess my question is, how to I casually bring it up to the family members my self? I came out in a facebook post, and a text to my bestfriend. Other then that, no face to face conversations.. Is there a good way to go about it?
Or should I just zip it till after Christmas?