I'm in a dilemma and I'm not sure how to make the right decision or what the right way to go about it is...

I'm 18. My parents are divorced and have been divorced for about 10 years. They still hate eachother immensely, don't communicate or co-parent with eachother, but instead communicate through me and my brother (which is AWFUL).

My mom's family has been planning a family get together party for a month and we settled on a date that will all work for us. Mainly, it's to celebrate my aunt, uncle, and cousin's birthday. My dad's family just planned a family get together on the same date that my mom's family party is...this is to celebrate my dad's birthday. My parents are very very selfish, so they will not move the dates. They also make me feel guilty.

I want to stop feeling guilty and people pleasing. What is the right way to go about this -- go to my dad's family party or my mom's family party? I considered splitting the day in half, but then it's a 3 hour drive and that's too much for me (also I'm done people pleasing). Anybody have advice or a perspective on this tricky issue? Thanks in advance.