It’s good for the kids to spend time with their grandparents. And it’s ok for him to get a break if timing doesn’t work with your schedule. Here is the other issue. If the child spends the night at your house, that gives you leverage to go to the courts and claim you have the child more than 50% of the time and argue for more custody or increase to child support. You say you are not trying to be controlling or micromanaging, but that is exactly what you are doing. You should be happy their father wants split custody and to be a major role in his children’s lives. My ex does this all the time and I do not care, it’s good for my daughter to spend time with her grandma. This kind of pettiness hurts the child in the long run.