What would be the most fair way to offer care services for relatives?

I have three living grandparents who are close to being in their 90s. They all live on their own, but are starting to have some trouble managing. I’m considering giving up work and helping them out, BUT I can’t offer this for free, as much as I’d want to. My family can’t really afford for me to work for free, but I could work very cheaply.

Here are the specifics of all 3 families (2 sets of grandparents and me)

My immediate family: Consists of me and my husband. I’m having a baby in September. I wouldn’t start working for my grandparents (if I did so) until December or January. I’m not sure how I’d work out childcare so far. My mother and Mother in law have offered to babysit one day a week. Also, my grandparents are fairly low maintenance so every now and then, I may be able to bring her along to at least one set of grandparents. I would NOT leave the child alone with my grandparents ever. The baby may make this difficult—but I’d like to try to work something out.

Grandmother A—Lives less than 5 minutes away from my house. Unable to drive and showing some early signs of dementia. Currently, I drive her to the grocery store and doctors appointments. It’s been difficult for me to work at my current job, go to my OBGYN appointments and take care of her at the same time, so I haven’t been doing as much as I’d like. Basically, she gets VERY lonely and needs a lot of company and interesting activities. She also needs someone to cook for her. If she doesn’t get enough attention, she calls people several times a day and starts to bother the neighbors.

Grandparents B—Live one hour away. Grandmother in excellent health and normally independant. She is the primary care giver of my grandfather, who is in very frail condition. I would be unable to do a lot of the physical work that my grandmother does for my grandfather, but I think “babysitting” my grandfather so that she could go out and run errands or attend social clubs would help her out.

Anyway, I’m not sure how to broach the subject and not sure how to ask for money for my services or how much to charge. I feel bad for having to ask for money from them, but I’d ask for less than I would a stranger.