I think the main reason it's hard for me to consider them being in the same room is that after the divorce, I had to hear both my Dad and Sister shit talk my Mom in front of me. My Sister always has an excuse to miss the majority of the holidays as she's forced to work in the service industry during the holidays and rarely gets time off.

As someone who has heard unfairly negative stuff said about my Mom coming from my Dad and Sister, I sort of feel like it's my responsibility to keep both sides separate to keep the peace, so to speak.

Of course, none of this I can really tell my Mom as to why it's awkward for me to be in the same room together since it would just make things worse for her to have to hear that.