I'm so sorry you feel like that
I read all of what you said and you don't seem mean to me, you seem really hurt and feel lonely
I think your family doesn't understand as much It hurts you
I think you should try to explain them what you just said, that for you Christmas is for family(and tell them she can come for another day but not Christmas), that if they don't do that for you it's like they don't care about you, tell them that you feel like she will steal your place and that you feel like they care only for your brother
If it's difficult to say outloud write it on a paper and give them
I'm sure your family loves you and cares about you
I advice you to see a psychiatrist if you don't presently so you can have the medication you need for your disorders
If you need to talk you can either talk on the forum or DM me