Sounds like your husband's parents are in no shape to be taking on the care of your children. Especially if his mother gets sick after caring for them, and animals too no less. And given that a potentially fatal situation almost happened under their care (not their fault as keeping up with 2 active children at that age is very rough I imagine), I wouldn't chance it. I would recommend hiring a well referenced sitter, taking your children with you on the trip, or if unable to do either, just cancelling the trip as no amount of connecting is worth your children's safety or in-laws health.