Aiw for not wanting to invite my soon-to-be sister-in-law's new situationship to my birthday dinner

My partner and I are sitting down writing this because we don't know what to do. My boyfriend's twin sister (let's call her Sarah) has been talking to a guy on Tinder for about a month. Now they're not officially dating, but they act like it. To add backstory, Sarah and I share a friend group and have been since before my partner and I got together. She is very good friends with my best friend, who we will call Daren; they've been really good friends for 4 years now. People ship them together even though Daren is queer and neither of them likes each other (Daren turned down the s years ago, which they've gotten over). Sarah met Chuck on Tinder, and they have been talking for about a month and a half. They decided not to be together for an hour about a week ago; within the hour, Sarah went to Derek to complain about why Sarah decided not to pursue Chuck. When they got back together, Chuck found out about their conversation. Sarah, Chuck, and Darren then had a conversation where Chuck was upset about Darren "shit talking." The convo didn't go well and ended in Chuck and Darren insulting each other, and Sarah only sticking up for Darren one or two times. Now Saeah is saying she doesn't want to go to my birthday party unless Chuck is invited. I don't want Chuck to go tho because of the things they said to Darren in the conversation between the 3 of them additionally, Darren doesn't feel like he can talk to Sarah. Because Sarah, let's chuck, read through all of her messages.

Edit: During the argument, Chuck kept bringing up how Darren wasn't able to hold down a relationship (Darren had broken up with his partner of a year and half a 1 a month ago)

Additionally, to clarify, there was no actual s***-talking; Darren just said that Sarah deserved better.

And that Sarah was her own woman and could decide who she wanted to be friends with.

Ps we are dyslexic