When my (ex) husband and I were both working we eventually employed a live in mother's help during the long school holidays to get over the childcare issues. We interviewed either face to face or by telephone depending on where they lived. Once we had filtered it down to 2 possibles, we invited them (separately) to spend a weekend with us.
We started the process in the spring if I remember correctly.
The one who eventually came to us carried on coming for the next couple of years.
This was our way of getting around the sticky childcare issues and school holidays, because there was no way, ever in a million years, I would have expected, or asked, either set of parents do undertake childcare duties for any length of time- other than perhaps the odd day here and there. It's easy to forget that your parents are not the parents that raised you, they're older, with possible health issues and with a life of their own. (Even though I trusted them more than anyone else).
The relationship between GC and their GP's should be one of love, joy, fun and the creation of a treasure chest of happy memories. I just feel that burdening GP's with childcare duties can easily sour that relationship a bit.
Unless of course you offer to look after your GC without prompting and are happy to do so.
The OP reluctantly agreed to looking after children and now unwittingly find they are pet sitting as well.
Agree with most of the others here, probably too late to back out of the childcare, but a big NO to the puppy.