What's fair compensation for a family caregiver?

My sister and her family (husband and 2 kids) have been caring for our father who has mid to late stage alzheimer's for 3 years. They built an in-law apartment addition on their home for him, at his expense, but they have otherwise not accepted any compensation for the care that they provide. He is dependent on them for dispensing all of his meds each day, preparing all of his meals, taking him out for a couple of hours each day for exercise, etc. I wanted to ask if anyone could provide a general range of compensation that's typical for someone in my sisters situation? Many thanks!