Hi Pamina - my PILs (or as I affectionately refer to them, the TITs) used to be rather like yours once for probably the same reasons. They're not brilliant now, but that's another story, but after I finally got really fed-up with running about after 6 people whenever they came to stay (and I include dh in that number because for some bizarre reason, whenever the TITs come to stay, he resorts back to being a child, mummy's little boy??) especially after they came to stay to help (ha ha) after I had just given birth to no. 3, and they did NOTHING, I decided to take action! Previously, whenever their laziness had driven me mad, I had taken to my room for a sulk - this never worked. Partly because when I re-emerged post-sulk, they thought I had gone off in a huff and was being a moody cow (you can imagine the comments they would make to each other - "Our poor son, being married to such a moody witch" etc) and also still nothing got done so it was all still waiting for me and I had wasted time in my room when I could have got on with it.
Anyway, my new plan was to tell them, but in the nicest possible way, what I wanted then to do. Obviously I had to pick my jobs carefully, because until fairly recently MIL never changed any nappies (and the first one she did change, she put on backwards and it fell off!) but through this approach, they have gradually got better, and though they've still got a long way to go, aren't too bad now.
I really think that when you've got them to stay for such a long time, in your condition and still working, and with a poorly child, you are entitled to some help and shouldn't be afraid to ask for it. Yes, dh should probably approach them first with them being his parents, but we know in the real world, this usually doesn't happen and it ends up down to you like everything else. I read an article once, that said that you should always start off with a compliment before launching in with what you really want to say to get a more positive response. Why not start off with, "It's so lovely to have you to stay blah blah..... oh, dd would love it if you bathed her tonight, read her a story etc" You've got a good way with words, so I'm sure you'll be able to get your point over in firm, but kind way, then it's over to them but at least you will have tried.
Ah, poor you, and you can't even have a drink (don't worry about that though, I'm taking care of your share for you!!) Bite the bullet and go for it, you'll feel better for getting it off your chest. My PILS are coming to stay in a couple of weeks too, but I'm ready for them