Why does SIL 2 want you two to "make up"? Is it affecting the rest of the family? Is it spoiling social events?
If not, I would just say to SIL2, you are both very different people and you think it best to keep apart. The other sister must just accept this.
I’ve been meaning to do a thread about this for a while: Myers-Briggs 📝
Have you ever done something once but never want to do it again?
How long can you stand on one leg?