Advice for in-laws dirty home?!

I'm really interested to know WWYD or if any other moms have been in the same situation.  I always knew my inlaws were messy, I just didnt realize HOW messy until we stayed with them for a period of time.  My DH made the decision we needed to stay with them after our apartment lease was up to save more for our first home purchase.  It was a HUGE eye opener for me and destroyed my relationship with them.  I felt extremely dirty living there which has made me really worried about my kids (1 & 3 yrs) being over there, especially overnight.  I learned quick that they do NOT clean, unless they are hosting a large gathering for a holiday/bday.  No vacuuming, mopping, sweeping, cleaning bathrooms...nothing.  I drove myself nuts cleaning while I lived there bc I couldn't stand the mess.  Unfortunately they never helped me, thanked me or even respected the fact I was cleaning their house bc they would go right behind me and make a mess.  My DH even redid their bathroom, floor and toilet, bc it had been leaking from underneath (for who knows how long) onto the floor and it smelled terrible in there! They are the type of people who drop jelly on the kitchen floor and just walk away.  Or spill something on the carpet and don't care.  Their carpet is almost 20 years old and stained beyond cleaning, yellow dog pee spots and all!  I spent an entire evening shampooing their living area just to have them traipsing in their shoes on the carpet the same day.  And their bedroom is from an episode of hoarders! Piles and piles of clothes, trash, papers, dirty dishes, you name it.  There's just a small walking path around the bed.  The most terrifying of the situation is that my MIL takes a TON of pills.  She keeps them in ZIPLOC bags, in her purse, on her nightstand, in the kitchen.  She loses track of them often.  I couldn't believe she admitted it to me but while she was babysitting she said she came out of the bathroom and my son was in her purse, with her Baggie of pills! She said she was "certain" he hadn't taken any yet bc she saw him just taking his pacifier out of his mouth when she ran over.  She even admitted that if she hadn't seen him take out his paci she would have had NO CLUE what pills or how many he would've eaten bc she has NO IDEA exactly whats in her baggies! I've even found loose Nexium pills by the couch while vacuuming! She's just so careless and messy it gives me anxiety when she's caring for my children.  My FIL has a mentality that scares me to death also.  I don't like how he picks my children up by the BACK of their shirt collar or that he once tried to convince me and my DH that he did NOT need my childrens carseats (they were 10 mos and 2 at this time!) to drive 30 minutes away on the highway to pick up my MIL. He said buckling them in adult seats would be just fine! I couldn't believe he honestly thought that was ok! Now it makes me wonder if he'd ever try that when I'm not around or what else he thinks is okay to do.  To make matters worse, my DH has a "my parents can do NO wrong" mentality.  He tells me all of this is no big deal and I'm just blowing it out of proportion. I don't know what to do bc he is 100% on their side in all things no matter what and its causing a giant rift in our marriage.  Besides the fact I'm a wreck when my kids go over there.  what do you do?!  (They are really good people besides all this stuff though, they'd do anything to help their kids and their families.  I just can't get past this OTHER side of them)