GA, it sounds like a nightmare situation. I don't dislike my MIL, but I wouldn't want her here for two weeks just after I'd given birth. I missed your earlier post - have you broached them not staying with you - or do they still assume that will be happening?
If they aren't staying with you, I would unplug the phone and not answer the entry phone until quite late on every day to allow you and your dcs some peace and space. If they don't like it, just tell them you were all sleeping. Keep it on your terms and don't let them dominate what happens.
I can't believe they would even think you'd get a babysitter for a newborn so you can go out with them! 
With dh, it might sound daft, but could you try what we do with ds1 - ie a social story. Basically, you just write out the whole scenario and what is likely to happen and then discuss it from each person's perspective - comic strip stylee works for ds, but that's not really necessary. 
Its a great way of getting people to think about things from other people's perspective and also to think through a situation and understand the likely outcomes. Obviously we use it in a very different way with ds1, but it a good tool for mediating situations with nt people as well.
You have every right to rant - come and vent as often as you need, we all remember what this stage of pregnancy is like and the last thing you need is more stress.
Morning Tink - we've just got back from toddler group, which for once was quite pleasant. Dd has finally decided she can go off and play without me being constantly less than 2 cms away from her, so I actually got some adult conversation for a change and the people I'm not keen on weren't there, which helped. It was very cute watching her ride around the hall with the tricycle posse. She's still a complete wuss if someone takes a toy off her though.
The sun has finally managed to break through the clouds and show its face here for the first time since Monday - twas bloomin' freezing in that school playground yesterday. So dd and I had a slow tootle up to the shop after toddlers and bought some nice salady bits for lunch. She has been a proper sweetie this morning, so much so, I am having to restrain myself from hugging her constantly.
I am shattered now and intend to sit on my backside rest until school pick up time. Both boys have to decorate a paper place as a Royal Wedding Commemorative Plate for a competition at their Royal Garden Party tomorrow, so it will be paintbrushes, glue and general chaos after school and ds1 won't want to do it at all, so that's bound to cause a ruck. The flipping school only told us about it and gave out the plates yesterday - complete pita.