When a person is brain damaged, before they are discharged, their families/carers are extensively briefed on what to expect. The person isn't doing nothing because she's lazy, but because she's got a kind of brain fog. Sadly, things like hygiene slip away because of this passivity. This is why Gary so readily agreed to take a shower--when it was brought up by someone else, the fog lifted.
The shushing is part of the difficulty of remembering what is appropriate in social situations. What person without brain damage would sit there and listen to James go on and on and on about how helpful and wonderful he was?
So, to sum up, I really think that BB should have briefed the HMs somewhat about what to expect, and I think that it would be a much different house, although some of them still would have been mean and nasty. After all, they're treating Gary like he's a nasty version of their granddads. I think Audley, for one, would make allowances. Then we'd see the real villains.
Another poster gave a really good source about brain damage.
http://synapse.org.au/get-the-facts/...act-sheet.aspx