What should someone expect as a care giver?

My daughter and her husband are care givers for an elderly woman and she lives in their home. The woman is her sister's mother in law. Her sister pays almost all of the rent on the house, but nothing on any utilities etc....My question is what is reasonable to ask for as far as days off, ( what time of the day should the day off begin and end?) When it is her day off the woman's son takes care of his mother at the house. They do not take her to their home. What would be reasonable to ask for? What about vacations etc....The son takes her for all doctor and dentist appointments. If I have overlooked anything please include. Hope someone can shed some light on this. I believe it is always better to cover possible problems ahead of time,so that all involved knows what to expect. I would appreciate lots of input on this . THANKS MUCH