Anonymous wrote:OP again. As odd as it sounds, I just don't think the filth registered with my husband until I pointed it out in detail. It was just how his house was and then he lived in a fraternity house and with a series of roommates who were likely no cleaner. He has risen to the occasion at our house, but only because it's important to me -- I don't think he cares one way or the other. Now, if something happened to one if the kids at his parents' house he would be crushed, but, of course, no one wants it to go that far. Plus, there's an underlying defensiveness because his folks are not well to do and I think (reading between the lines) that he thinks I'm being a snob. I don't think there's a correlation between socioeconomic status and cleanliness, but that's what he seems to be hearing.
I've been there and it's hard. While I completely see your point, I think it would offend the in-laws beyond belief and I don't think the cleaning crew idea beforehand would work. This is what we did when we were in a similar situation a couple of years ago (and this works if your kids are young, but harder if they are older). I clean as soon as I get there. I pretend to "nap" and then I get to cleaning the bedroom/bathroom. The day we leave, I arrange for a cleaning crew, because "Little Johnny is so messy when he eats, and I can't possibly leave them with all of that mess, and I didn't want to take away from our time together by cleaning." (My kids are actually really neat, and we always clean up after ourselves, but this is a good way of getting in a cleaning crew to do a deep clean at least once a year.) We get recommendations from neighbors and speak with the crew ahead of time.
We also buy them sheets/towels as a thank you for their hospitality. Last year, I bought one set and showed it to them, and said that I found them on super sale (again, trying to avoid the snob issue), and that I though they were a perfect match for their guest room. I said that if they liked them, I would go and buy a second set to match (there are twin beds in the guest room). They liked them, I ran to target, got a second set, and washed them and put them on the beds to help out. With or without a cleaning service, I also strip the beds and wash the sheets after I leave. Now that might not help you next year, but it gives you peace of mind for this year.
Our child now has relatively severe allergies, and we now do have a true excuse not to stay with people.