S.T.
SOmehow close family does not think of themselves as being rude. This get-away place - did you pay for it entirely by yourself or did your inlaws help pay for it anywhere along the way? I find that when strings are attached at some point they stay attached.
When I was pregnant with my first child, and my husband and I had just bought a house and were frequently working on it on Saturdays & Sundays my inlaws began just showing up. They'd "bring a meal" as a way to give the impression that they were being helpful - but the meal was always take-out of some type that we could have easily order on our own. I think the meal-bringing was more to make themselves feel better than to feed us becuase it was almost always not the kind of food we'd eat. I recall one evening after work on a July Friday, laying down with my swollen 8.5 months pregnant legs up - wearing just a light housedress on - no bra, even no panties - and there they would be - at the front door! I made them wait until I could get some clothes on (my husband wasn't yet home from work) and I told them I had no idea to expect them, that I hadn't been decently dressed and I wish they would have called to ask if this night was OK or not. All with sweetness & light in my voice while giving them hello hugs and kisses. Then I added that I hoped that once the baby arrived they'd realize to set up times in advance. And that was that. We never had that issue again. it was taken care of right away, in person and with kindness and winsome-ness.
I suggest you give them a call - and in a sweet tone tell them that your DH just let you know they would be there - and how surprised you are! Tell them normally it would be so wonderful to see them but that you are exhausted, not feeling well, focused on _____ (whatever) and that you're sorry but you don't even know what to say. allow for a pregnant pause and see if they take the hint. If they don't there's nothing you can do about it - your DH has already OK'ed their visit.
By telling him that his parent were rude you put him on the defensive - that never works out well becuase he'll try to defend them. Basically by OK-ing their visit before talking to you he invalidated your feelings - made you feel like he doesn't think your feelings, needs for rest or opinions are important. You felt hurt and responded that his parents are rude (even if you didn't say directly that they are rude it was implied). He felt that you don't place any value on his family and so the dance began... Of course there would be an argument - you started from separate places.
If you're stuck with them this week - so be it - what can you do other than be gracious and let them know you have lots of other stuff to do. If this week is beginning-of-season cleaning enlist thier help - assign tasks (clean the screen, dust, pull weeds, etc.) If they offer to help accept their help and assing them things to do. Don't let it be their "son&DIL resort" getaway.
Good luck - dealing with relatives is tricky!