That sounds really rough. I've always considered the kitchen "my space" since I cook most of the meals, so I try to keep the counters clean and free of clutter. My husband is incredibly absent midned and disorganized, so he will throw all kinds of crap down on the counters or table, even if I just finished cleaning there. I've started taking his crap and putting it onto his desk. Passive-aggressive? Maybe. But that shit doesn't belong in the kitchen. I'm sure he doesn't like having random shit dumped on his desk (even though it's his) any more than I like having random shit strewn about my kitchen. Anyways, my point is, take the stuff off your desk and randomly dump it in their space (bed, couch, kitchen, whatever). Are you paying rent or a portion of utilities to stay there? Because if they try to argue about it being their house and that's why they put it on your desk, you can counter with the fact that you also pay rent/bills so it's your house too.