How do I get siblings to share responsibilities?

We have a Dad, mild vascular dementia, who is 85. 3 daughters and one brother. I am one of the daughters. When my Dad had prostate cancer 2 years ago I was him primary caregiver who took him to all his appts, ordered his medicine, took him to specialists. I work full time and we all live in the same area. My sister is retired, and my other siblings work like I do. I work from home, and my boss (at the time) told me to take time during the day to help my dad and do work later so no siblings had to help at all. My Dad had foot surgery and had 4 appts a week. I Took him to all appts, ordered all his meds, kept up on all his insurance---did everything while keeping up with my full time job. Then Game changer---I broke my foot. I have been told 6-8 weeks for recovery and im only 5 weeks in and my siblings want to know what my doctor says about healing, when I can return to help. I had NO vacation this year, No time off from caring for my dad, and both sisters and brothers took 2 week vacations, and both my sisters were sick too. One had pnuemonia for 2 weeks and other sister broke her wrist. My brother had major surgery and was out for 7 weeks. No one was pressured to heal sooner, but I am being so. Also the time amounts each sibling spends with my Dad is different. My dad lives in a senior living place in his own apt. and my sister spends 45 mins in the AM 5 days a week (she is retired) and my other brother goes for 2 hours 3 times a week. My other sister has him over for dinner on Sunday and goes 1 night a week. She is the one who puts the schedule together. My schedule before I broke my foot was Tuesday, Wed and Friday night for 2 hours, Saturday from 1130 to 4, Sunday at 7 to pick up for church, home by 11AM. I suggested we look at the amount of time we spend to be added up to keep it all fair, and was shot down. I suggested we speak to a counselor who has dealt with this before to get ideas on how to handle and equal the amount of time we spend with Dad. No one wanted to go. What else can I do to even up the Dr appts, times with dad, and everything else? Ideas??????? Thanks for listening.