Lanie, don't mind this, its a combination of my medical training and personal experience.
Ok, here's a few ideas. I actually found this site very tremedous help when I was caring for gma.
First, don't quit. Stand back and let your sister try. When she fails, simply say "are you sure you don't need any help?"
Second, call Adult and Family Services and ask to speak with the social worker in charge of elderly. Nothing is wrong, but you as an in home caregiver are granted services. Services of many needs such as: a break to do things you want whilst others care for him in his home, food services, cleaning services, respite care, support groups, so on.
Third, I am not sure if this applies, but ask the doctor if a med adjustment is in order. The only reason why I bring this up is because Gma has vascular dementia and I was telling Lanie all the things and everyone else that was happening here, and it was suggested that Gma may need a med adjustment. A few weeks later, it got to the point where I was actually being strangled, beat up, punched, and more. After 20 minutes (when the doctor said only allow 10 before calling 911) I gave in and called 911 on my cell. I stuck the phone back in my pocket and hoped the dispatch heard me. Thankfully they heard me saying things like "grandma please stop hitting me", I just said it like that and whatever she was doing. I then said "grandma you live at ___". I did it that way because I heard if they are in an aggressive mood that it can provoke more behaviour. The police and paramedics came. They took her to the hospital where she attacked a nurse, actually physically threw the hospital bed matteress at a nurse, managed to escape the bed netting, and was put in restraints and admitted to the physc ward. It was then my mother, Gma's power of attorney, finally believed me that she needed a med ajdustment. This new medication is a godsend, I love it. Be thankful you have your sibblings to help, I was taking care of gma 24/7 and only got my mother to give me 3 hours off a week.
Also pray, if you do.
"The Walking Medical Mystery"
Too many Allergies / Too many RXs & DXs
A Rare Gem for Doctors and Guinee Pig
~Medical Caregiver and Doctors Worse Nightmare~