Where do I draw the line?

I cared for a parent diagnosed with cancer years ago. From the day of my parent's diagnosis to the day he died, I was with him just about 24/7. My other parent had a hard time dealing with what she was facing, so she was grateful that I was able to stay with him all day and well into the night during his hospitalization. He died roughly 2 months after his diagnosis. My other siblings came and went due to their schedules, one sibling living out of state. I just about physically collapsed after his passing. It took me a very long time to recover. I also did a great deal of caregiving for a grandparent. I took her to the doctor every month for check-ups, stayed with her in the afternoons, fixed her lunches, called her daily. I was with her for many days and hours when she had a major stroke, and was with her the day she died. I oiled her feet and combed her hair before she went to the emergency room and I held it together just long enough after her death to pick her funeral gown and make arrangements for her service. My mother was too out of it and I didn't want her to deal with funeral arrangements in her condition. I had a special relationship with my grandmother, so her passing took a major toll on me for many years. Then my mother was diagnosed with dementia a few years back. I was the sibling who made sure she was admitted and evaluated, and she was released to my care on discharge because it appeared to be the easiest arrangement based on my circumstances at the time. I cared for her when she was very violent, depressed and unbelievably challenging to care for. I did this for a couple of years, got her stabilized, got sick, got in touch with one of my siblings and told him I could not continue caring for our mother. My mother has been living with this sibling for several years and he took advantage of her in an inexcusable manner. He doesn't seem to care though, believes he was entitled to do what he did and is unapologetic. Now that he's taken advantage of her and can no longer benefit from the situation, he's been suggesting that her care has not been balanced, he needs a break and of course the sibling who should take over caregiving is me, since he dumped his adult child on my other sibling and doesn't want that arrangement disrupted. I feel as though I've done way too much caregiving for very ill relatives over a span of many years. I can only take over my mother's care again, if certain basic conditions are met such as having in-home assistance and making sure I do not have to carry big expenses for medical supplies, prescriptions and doctors -- all of which I'd paid out-of-pocket for while caring for my mother. Now that I've communicated my needs, I'm being ignored by my other siblings. It's getting ugly, my husband is very concerned about me, and I'm at a point where I feel as though I might not be able to do this again. Where do I draw the line?