Why are my inlaws so filthy?

My common law husband's parents are the most filthiest people I have ever met in my life. They DO NOT like to bathe, and it isn't because they are old. I was told by a relative that they have never liked to bathe. They will not use the A/C in their house, and they have roaches crawling everywhere in the house, even over the eating utensils. My father in law even had roaches laying eggs on his skin. I can't believe their doctors hasn't noticed the smell. Nowadays they won't even brush their teeth, and my mother in law's breath is like a rotting corpse. How can these people live like this? Should I report it to the necessary authorities? My husband has tried everything, including building them a walk-in shower stall, with handle bars, but it has boxes stored in it. They won't use it. I get nauseated when I go over there, which is rare. The roaches are so bad, I had one fly right into my face one time, and my old mother in law just laughed. I think it is time for human services to get involved. I just don't know what would happen if a case worker visited. Would they take them out of their filthy environment? None of my husband's brothers give a care. One of them even lives there, and doesn't bathe either. I am at my wit's end with these people!