Trauma at the holidays, how to cope?

I have cPTSD from years of abuse from my mom. I avoided her for years, but the past 5 years or so, I helped with my sister's Christmas because my mom is very poor and is on disability for her hip. I was under the impression that she'd changed and treated my sister well. I couldn't manage more interaction than that at the time without being hospitalized.

Early this year, I agreed to help watch my sister while my mom underwent a surgery and would be staying at a nursing home for an extended period of time. During this time I essentially learned that my mom had become a serious hoarder, gotten very paranoid and had become delusional (everything is a conspiracy). My sister had been living in literal squalor, had failing health at 16 and spent most of her time sleeping on a couch in severe depression. My mom had babies her completely, and not like in a cute way, she couldn't do simple things when she came to stay. My boyfriend and I agreed that it would be best if she stayed with us. My mom also agreed, begrudgingly, knowing that CPS would never allow her to stay in that home.

We've worked to try to get her normalized, figure out her health issues, make sure she's eating okay/etc but she's at the age she has to start learning to be an adult and I know that's hard because I went though something similar.

I went from working, making art, streaming and teaching to taking care of my sister,which was a big change for us and we are trying to learn along the way. She's an amazing person and I love her. I hate that she went through all of this.

My mom doesn't realize she's abusive so it's hard to deal with (that is the short, nice version). Her reality isn't the same as everyone else's. I'm still triggered when dealing with her, especially around holidays. She called me tongue screaming about something that wasn't my fault and canceled coming to see my sister. She did the same thing on Thanksgiving.

I'm trying really hard to actually make this a good holiday for my sister, since she's used to celebrating, but I stopped doing so years ago. My family ostracized us because of our mom and when I left the house 20 years ago I no longer felt the need to keep up appearances.

I'm trying to make our own rituals I guess. We aren't Christian or anything but she wanted a tree. I have made some ornaments with her and offered to try holiday crafts or make some deserts but I'm out of ideas and honestly it's really hard for me to do these things.

I've been asking people this in my friend's group, but I'll ask here : what are some things you like to do as a group /family over the holidays? How do you cope with holiday trauma? I only ever remember them as times I got hurt the most.

TL;DR what do you like to make or do during the holidays, and how do you reconcile bad past feelings about a holiday you want nothing to do with while you're being actively accused but also want to shield your loved ones from it?

Image : skull ornament we made fire the tiny Christmas tree, which she requested in black.