My sons' In-Laws are dirty people; babysitting my granddaughters. Please advise.?

My two small grand daughters, one is eleven months, the other two and a half years. They get babysat by my sons' In Laws and they live in a tiny 1200 ft space, usually containing three to four adults. They all smoke inside, and it smells of stale food and trash. I don't think they own a vacuum as their floors are filthy with dirt, leaves, and animal hair and I have to tolerate these two beautiful girls going over there. My son was not raised to be a slob and I cannot grasp how it doesn't seem to bother him. I don't mean to sound like a snob but it really kills me when I know they are there. I have had to drop them off once and the look on my granddaughters face killed me. I cried the entire way home cursing my son for putting them and me into this position. What to do?