Someone is going to eat a bitter pill here. Probably all of you will because all of your boundaries will need to adjust. Give up the 1% and have someone manage the trust. Your sister and mother are going to end up resenting you. It will destroy the family. For $23k a year I'd rather have them hate someone else. Have a 3rd party manage a traditional 4% withdrawal rate and let your mother spend the money as she likes. Stay out of the finances between mother/sister. That relationship is set and likely won't change.
Sis already has resent towards me and our older sister as we're "successful" and have relative financial security. Granted, my father setup my older sister, but I went to work for a tech company in CA around 2004 (use your imagination). So, younger sister feels she has to compete or cannot keep up with either one of us. Personally, because I have that much more (no bragging), I feel she has more resentment towards me. I offered to help her get a job in tech., just she doesn't want to study STEM or get a MBA in the sciences. There is little I can do with a Humanities degree in technology. So, again, she feels lost and angry.