YANBU op at all.
When ds1 was a year and I was going back to work, my parents offered to have him (argued to have him I should say). We needed cc for three days a week.
We talked about it for weeks, I did several checks of 'are you sure', 'it's a lot to take on' etc - they were adamant and we were very grateful.
BUT, in practice it was very different. It was always thought of by them as them doing us a favour. They were 90% reliable, but if there was the odd two days they couldn't do that 'favour' then they didn't feel bad about giving us a weeks notice that they couldn't have ds next Monday and Tuesday for instance.
Which dropped us in the shit on a regular, if unfrequent, basis. He wasn't registered with any nursery or cm so we had no back up when this happened, and we'd have to take AL or call in sick.
After about 18 months, my mum dropped on us that she'd be unavailable for a week in November - with a fortnights notice, but by that point we didn't have enough AL left to cover it. DH works in retail, it is much more inconvenient for him to be off work at that time of year than me, so I ended up calling in sick for a week as I had no other option, and had a bollocking when I went back.
In the New Year I sat down with my parents and had the 'i'm really, really grateful but if you want to continue you need to be 100% reliable' conversation. Awkward. It turned into an argument, they couldn't see my pov at all.
It ended in us not speaking for 2 months and ds1 starting at a cm. 5 years later, it's behind us, but the dc going to a cm is the unspoken elephant in the room and I know that my mum still harbours some resentment about it and sees it as an ungrateful slap in the face from us.
I would never, ever use family as regular childcare again though because it's a bloody minefield.