We learned the hard way how to make visiting the grandparents work better for our baby. We have my mom pick up the kind of baby shampoo and lotion that we use at home so there are no allergy issues. We also bring our own Pack and Play crib so our baby sleeps in a familiar place. We loosened up about the schedule as we all wanted to do one fun thing per day. We planned it in the morning and just let the baby sleep in the stroller and carseat. Then in the afternoon we stayed home so the baby could get a really good nap. We found that being out all day made for a really crabby baby, but getting one really good normal nap in the afternoon was fine and a shorter nap in the morning didn't matter that much.
We also brought lots of extra toys and some that our baby hadn't seen before. We went out with my mom to some of the second hand stores and garage sales to buy toys and books and keep them on hand. That worked really well. She now has one closet where she cleared a shelf for items to pull out when we visit.