Hello London1298, welcome to the BB forums and for posting a disappointing situation for you and your sister.
For me to have a conversation with my step mum wouldn't matter because she was too loud, demanding and everything had to go her way, a distant cry from when Mum and Dad's marriage was a viable one, although I was married when step mum appeared, so it's slightly different to your position, but the principle is certainly similar.
You have a mum who undoubtedly loves you, different to your step mum who seems to get what she wants, swims in your pool and does seem to be jealous of your mum, that's what you should be proud of, your mum has better connections with your side of the family.
I'm sorry about what happened this Xmas, because all children should receive an equal amount of presents and when this doesn't happen, then how could you possibly enjoy Xmas day.
Can I ask if you were able to ring your mum, tell your dad that you want to be with her, simply for the reasons you've pointed out to us, no child should feel unwanted like in a situation like this or at all.
If you tell your dad then hopefully, he will know exactly what's been happening, so I'd like to know how you feel.