What is the going rate for family caregivers?

Are you talking a few hours a day or a few days and nights at a time ?

Will you have an employment contract with these relatives and pay social security taxes and carry workers comp insurance ? Or are you expecting to make them a gift which could be set aside if your parents ever need to file for Medicaid ?

You can check websites to see what going rates are in your area to hire a caregiver directly
If you were to hire through an agency the fee reflects the caregiver cost plus taxes and insurance and their profit
Since I assume your relatives are not trained health professionals I wouldn't think there's much premium over other low wage hourly jobs

The pay is whatever your parents are willing to pay other family member to help out. Best thing is to create an employment contract saying how many hours, what are the duties, and what is the hourly rate.... this would come in handy in case in the future your parents need to apply for Medicaid.

In Michigan I think a fair family rate would be $10-15 unless the work is very intensive. If it is just for a few hours, I would treat it like paying a babysitter. No need to make it complicated. If it is more like a part-time job, you would want to consider a contract and employee provisions to keep everything traceable and legal.

BTW, if it is your siblings doing the sitting, I would pay them the same thing you get paid.

So what would this employment contract have to state?

Here is an AC article with an example of a caregiver contract in the PDF attachment.
https://www.agingcare.com/articles/personal-care-agreements-compensate-family-caregivers-181562.htm

Cowpatti, also don't forget what MsMadge mentioned above about "workman comp"..... this would be a rider that your parents would need to add to their homeowner's insurance. It is very important to have this in case whomever is being paid to care for them becomes injured on the job.