How much should I charge my grandfather for care when he is in a facility?

If he’s in a facility, you cannot charge a fee for caregiving. The facility is doing his caregiving. If runs are needed to buy him toiletries or new clothes, family does this out of a sense of familial duty and for free. Some NH can place his personal needs allowance set up at the NH to be used by SW to purchase items routinely from a checklist at a nearby Walmart type of store.

But if he actually has business & real estate that needs management which you do as within your dpoa then you could be paid from the assets for this. There should be some kind of property management agreement done with rate set and paperwork all legit notarized with witnesses.

If you are talking about your duties as POA read the document carefully, some expressly prohibit any payment.

Why would you charge your GF anything if he's in a care facility?

I think there needs to be way more detail to this situation.

Isn't the facility caring for him?