I have been in the same situation, and always chose my mum...except last year...when h2b and I went to the canary islands for some festive holiday sunshine. I remember feeling rotten for it, and even though I knew my mum had people with her, I still felt rotten. Now my mum is no longer with us, and I do regret going away last year, but I can't change the past...and I done it because h2b and I wanted to.
Anyway, I'd say stick to your guns...I know h2b and have spent xmas apart a few times because of the family issues....is that not something you'd consider? We saw each other xmas morning, but not til the next day...and to be honest, it worked fine because we see each other everyday.
Hope everything works out for you lady...keep us posted.
X