Family childcare didn't work for us.
Firstly, they weren't prepared to follow our routine and overloaded the DC with sweets/crisps/McDonald's and generally spoilt them rotten. Nice once in a while, but 2-3 days a week - just no. Picking up a fractious overtired child who hadn't napped because it didn't fit into their routine so they'd pepped him up with Haribo made our evenings a fucking nightmare tbh.
Then we'd have last minute phone calls (the night before) saying "oh sorry I can't have DS tomorrow, Betty has asked me to go out for the day/I've got a hospital appointment/we're spending the day sorting out the garden/FIL and I have had an argument and I'm just not up to it" meant one of us taking last minute annual leave. Employers were not impressed.
And because they're family, and they're doing it for free, you're expected (on here at least) to be everlastingly grateful and put up with anything and everything you're not happy with.
I should point out that, like your wife, we never wanted to use the grandparents as childcare, they insisted - but regardless, anything you don't like or are not happy with - you're expected to just suck it up.
We lasted about 4 months then put the DC into nursery.
If it ain't broke, don't fix it.