Sorry this is so long, I was trying to put as much detail as possible!
MIL is older and has some health-mobility issues, she needs 1 or 2 canes to walk, can't really do stairs (she can but it takes her a long time), can't walk and carry a purse, can't bend over to put on her shoes, etc. FIL is fine, gets around, healthy, strong, etc.
When our twins were ~8 weeks old, we had them come over to babysit so DH and I coud go to a dinner party (thier first time). MIL and FIL have to come together since MIL can't do much physically, so FIL was the main care provider. They called on their way over about dinner, DH said we had frozen pizza or soup and sandwiches for them, MIL said she would just have FIL run out and get something because that didn't sound good. DH said no, that isn't a good idea, we would prefer it if he stays here with the kids. So they get here, we show FIL the food, how to put the kids down, etc. and leave. We get home and are chatting, kids did fine were upstairs sleeping in the nursery, no issues. However, they said that FIL had run out to get them food after the kids were asleep leaving only MIL there. DH and I were both furious, and her response was oh they were fine, they were asleep the whole time. Of course they were fine, but if something had gone wrong or one had woken up, or they had started choking, or any hundreds of other things that could happen while FIL was gone, MIL would not have been able to 1) get up the stairs to get them, or 2) pick them up out of the crib.
So fast forward to now, they are 11 months old, we have not asked the ILs to babysit since, and they keep giving us guilt trips about it. If we have a babysitter when we go out it has been my parents, my sister, my BIL/SIL, or our nanny. We initially expressed our anger/disappointment with them, but haven't brought it up again since that night, when they do guilt us, DH usually just gives some excuse for why someone else is watching them.
They recen't gave us a nice GC to a restaurant and a babysitting coupon. I know they love their grandkids and DH wants them to be able to watch them, but I keep telling him that I can't trust their judgement, but I am starting to feel guilty and have second thoughts about maybe giving them another shot. WWYD?