Wow nocode, I think that's a great idea to help others over the holidays. I am so sorry she is disregarding the importance of your time with your sons. And yes, I think if you have one more incident where you feel she is pushing you aside, you will have to get something in writing. It seems like she takes days and times away from you but doesn't offer anything in exchange, like an extra day here or there. That makes me sad for you and your boys.
Don't forget (and I know you won't), your apartment is just as warm and cozy as the house (YOUR house, I get that), because you, Daddy, live there.