How to I handle my narcassitic mother's behavior towards my mate?

My mother is 88 and very self-centered, queen bee. I work during the day and my mate has been helping her do her errands, helped her with hours of remodeling, and landscaping managing all the workers. Recently, she has moved close to me with my father who is 92, around the corner, which is not working out. I have appreciated my mate helping my mom tremendously. They both are very opinionated and they get into discussions and argue as to who is right. My mate will not back down in the disagreement and neither will my mother. Instead of allowing each other to disagree ,my mother recently indicated that she is no longer talking to her. She is not going to talk to her anymore at all.

I have been trying to make them happy during the holidays and invited them recently to a special dinner. She refused to speak in the car, and during dinner only spoke to me. I wish she would of told me I would of canceled. I felt uncomfortable with her game and so did my mate. It was rude and uncomfortable. She says that my mate is overpowering and needs the last word. Well, I think actually she is not used to not being right.

My mate has done so much to support her, with hours of care and errands and now she is treating her like this because she can not always be right.

Christmas is coming and I do not even know how to handle dinner with my siblings coming and their mates with her behavior. My mate does all the cooking each year for the family, and we through the parties at the house.

Now, with her acting like this --I am not sure how to handle her. Or if I should even talk to her about this? Maybe, it will make it worse to confront her on her inappropriate game. I just am at a loss and do not want to ruin xmas with this.

I feel deeply hurt by her behavior and need to be right and unwillingness to consider others feelings. I feel hurt that she is playing this no talking game with my mate and feel angry because it is inappropriate. Having my parents over, especially since she is cooking and preparing the meals does not feel right when she is acting like this. I feel deeply hurt because I have tried to hard to please her and act in good faith. Just another disappointment with my selfish mom.

I need boundaries with them and recently I told her that it is no longer acceptable for them to argue infront of us. They argue infront of us and it has been very uncomfortable . I am not sure, but I think she was very offended, that I even brought this up. Anyway ,maybe she is getting back at me. Any suggestions on how to deal with this situation?