I made it perfectly clear that people who 'just turned up' wouldn't be coming in - we just ignored the door.
A few times my sis and parents rang to say they were in town and could they pop in - that was fine, as was the people who pre-arranged a day. I would only have visitors at the time of day I knew DS would be settled, then he could be passed around without having a meltdown - better for me and the visitors.
My MIL was fab after DS - as soon as she arrived she went straight upstairs to give DD her dolls house furniture (which she bought for the occasion) and played with her for about half an hour. She then came down and had a hold of DS. She must have been dying to give him a cuddle as soon as she came in, it was one of the few times since I've known her that she used her common sense for a change!
You just have to be brutal, I have a terrible habit of hogging DS, under the pretence that he's coming up for a feed or he needs to go to sleep, nappy change, or I just used to wander off with him or ask visitors if they fancied a walk to the shops with me so he could 'get some fresh air'.
There's a million and one ways to keep a hold of situations like these, you just really have to put your foot down (even when you don't feel like it).
I think it's truly awful that they let you stand with no-one offering a seat for you post-section. In future just say something like 'mind if I sit down somewhere, my stitches are starting to hurt/feel faint etc etc' - have a word with your DH/DP too so they know the deal and back you up.