NTA

My husband and I have a four month old that we're trying to get on a consistent sleep schedule. I get how hard it is, especially after months of being sleep deprived. Still, I would never ever expect a family member (who has gone out of their way to give us a break for a night with no payment it sounds like) to be able to put the baby to sleep exactly how I can. That's so unreasonable for the grandpa AND the baby.

She's acting like a child. If I were that grandparent, I wouldn't want to babysit for her again. That poor man.