She sounds like she is being very considerate indeed. If she is "not very good at picking up social cues" your DP just needs to be very straight with her. And do it now- have a chat on the phone and say"it will be lovely to see you Mum, just to let you know that Forever will be pretty tired (as will I probably) so we won't be up to long visits, and of course we don't know how long the baby will have been with us by that point (if at all, ha ha), so we will have to play it by ear. I bet you can remember what it was like when I was a new baby, can't you?"
I wouldn't worry about the husband- he's probably as uncomfortable about the thought of you getting your boobs out in the same room as you are. Again, just brief your DH to stage manage this either by getting him out of the way "Bert, can you come outside and help me with this problem I have with the garden hose?" or by explaining that you are more comfortable feeding in another room and that it might take a while, and keeping them entertained while you do so.
My first baby is due in 2 weeks. MIL and FIL live 3 hours away. We've been clear that they can't come to stay until at least 2 weeks after the baby is born but they say they may come up to meet him briefly a bit sooner, on the understanding that it may be a v short visit compared to the length of their journey. All are fine with that. SIL, who lives near her parents and has kids of her own, has been v helpful managing expectations.
Your PILs are adults, sure they can amuse themselves away from your home over the visit. Perhaps it's 2 nights in the hotel as they plan to arrive late one evening, spend a few hours the next day with you, go out for a nice meal and head home the following morning?