Are we entitled to per diem?

My husband and I are on site property caretakers for an elderly couple. Part of our job requires us to drive them around - sometimes a day trip, sometimes overnights. Can we deduct per diem if they don't cover all hotel and food or can we only deduct exact expenses? How far must we drive (or be out in a day) to qualify to take a per diem deduction? We are ready to go on a 2 week trip and can be off on our own for a couple of days between stops. While it is our time, we are still required to be away from home for them. Can we deduct all expenses? Thanks