I understand your concern. This sounds a bit like my H. My in-laws are at our house every day watching the kids. They are happy with this, they've offered to do it, so I can work. H loves this situation, but I dislike that he takes advantage of it, by staying at work as long as possible, and being involved in several different societies, meaning he's off at meetings several times a month, so the in-laws are often there with the kids from 2 - 9pm.
In addition, if I'm gone for the day on a weekend, I know full well that H will have the kids at his parents.
At one point I tried having a neighbor girl come in one day a week to take some of the load off the in-laws (76 and 80 yrs). H complained constantly that he had to be home by 6pm, and that he often had to feed the kids (!). He once called me to ask how to feed them (I make dinner before I leave in the afternoon, so it's just a matter of heating it up and putting it on the table.)
Do, please, try to find a way to talk about this before it becomes a greater issue. Along with the money issue as well. H took over our bills 5 yrs ago when we moved in here, for the same reasons. He's a perfectionist, and couldn't deal with not knowing where every penny went. I hope you are able to sit down and work on a budget that will keep him happy.
I don't feel I'm in a position right now to give advice. But I do hope you are able to work it out before it grows into a monster. It sounds like you're well on your way.