Sj where as I can understand your concerns that your m.i.l. may not respect your wishes I also found you OP rather harsh and uncompromising.
I think it's only right to make you aware that I have been estranged from my youngest son and only GC for more than 5 years.
When his wife became pregnant I was asked if I would help out with childcare and jumped at the opportunity. It was agreed that on the days I was to have our GC I'd have him at our home. Mr. S. and I spent a lot of money so that he would have everything he needed to be safe and well looked after. We even bought a baby monitor, not something we'd used for our own, but something they wanted us to have.
Before we were eventually cut out, we were told that he would no longer be coming as he'd been booked in with a child minder. I am crying as I type this paragraph as the pain of packaging every thing up that we'd purchased,so it could be returned, is a raw now as it was then, 5 years ago.
I ask you to be careful, to talk things over with your husband and find ways of dealing with the issues that bother you, together.
You say that you 'deal' with your mother. Mother's and m's.i.l. aren't to be dealt with, they're to be engaged with and listened too. You may find that if you engage and listen to your m.i.l. she may be more willing to engage and listen to you.
I hope for all your sakes that some resolutions and compromises can be found. For your m.i.l., having offered to do childcare for 3 days a week to then learn that your child has been booked in full time with a childminder, will be a painful and hurtful slap in the face.
I know, I still remember the pain of that slap and probably always will.