My in-laws are always staying at our house on the weekends - without asking me. How do I say "no"?

My in-laws live about 3 hrs away from my husbands & I's house. It seems like 1x per month - they find some reason that they need to come to our area of the state and plop their feet up at our house for the entire weekend. Lately, their visits are becoming more frequent -- 2-3x per month. My husband and I are very busy - and work opposite schedules -- the weekend is all we have together. And when this crew comes into town - they bring husbands, wives, the mother-in-law and their children. It's like we're a new vacation home for them. I understand that family comes first - but I'm having a hard time enjoying their company when they're always around. They were raised differently then I - they rarely say thank you for meals, never help to clean up, and never say 'thank you' for us allowing them to stay. That makes it all the more difficult. Even worse, my husband is always very excited to have them there - so I just put up with them....again, and again, and again. I need their visits to slow down - but I don't want to be rude and make my weekends and theirs miserable. Should I just be honest and ask them to please back off with their frequent trips? These trips are even more frustrating as I generally find out about them coming 2 days before they head our way - which changes any plans I may have made in the first place. Of course, they never ask me - they always TELL my husband they are coming. HELP HELP HELP with a little advice of how to cure these bad habits these people are starting before it gets worse!! I want to enjoy these people - not despise their company!