Can you maybe put a little reference guide together?
Including routine specifics (ie, sleep/wake times, and how he goes down :we read this book before nap time, and put his lovey, Poo Bear in bed with him, etc.), activities he likes to do, when to brush teeth, bedtime routine, how much if any TV, what helps calm him if he gets upset, what his meal consist of, how much water/milk/etc. Also include all your contact info, emergency numbers, etc.
Good luck and enjoy! It's great to have family who can pitch in!