Well, first of all, if that had been my pup at the family Thanksgiving, and a child would not listen about leaving it alone, after the third time telling her, I would have kept the dog on my lap or in my arms or would have taken it home. I can understand the in-laws being upset about the bite----it was their CHILD that got bitten, and in the face. Don't want to upset you, but you were the adult present when this happened, and you probably should have separated the two before it got to this point. As far as the second bite incident, again, you have every right to be upset. It is your CHILD that got bit. I think the in-laws didn't act concerned, because they are still harboring bad feelings about their daughter gting bit by your dog, and they may feel that this evens things up------that doesn't make their lack of concern right.
I think that everyone else is making the right call on this-----no more dogs at family gatherings. But, I do think you should just let this latest incident go. "Divorcing" your in-laws would not be a good solution, as the children would be the ones to suffer. I should know, as my father and maternal grandparents had a falling-out when I was very small, and my father would have nothing to do with my mother's family for 20 years or so. I always had a melancholy feeling at holidays as my classmates talked of going to their grandparents for Thanksgiving, or spending vacations with their cousins. I had no living grandparents on my father's side, and no cousins-----I missed out on a lot. Please don't do that to your children.
My husband's family do bring their dogs to some family get-togethers, and I did have my chihuahua at my MIL's for Christmas Eve. However, each person is respnsible for their own dog's behavior, and I always either have my chihuahua on my lap, in my arms, or my hubby or one of my sons has him. We do let him get down----with proper supervision.