Thanks for the replies all! I'd like to explain at least on our part how it's got to this stage - as I agree it's ridiculous that he can't do anything for himself! As some people below have mentioned similar.
His mum walked out on him and my DP when he was 1. It was such a sad situation, as he was without his mum for a long time - but not only that, DP lost the love of his life out of the blue (she'd been having an affair and left them for AP). He was depressed and on meds for a while, juggling work, being a dad, keeping the house sorted.
DP had to work full time obviously to keep the house etc and was hugely lucky in that his parents would take DSS each morning until he finished work; and he picked him up again at 6. So that's every school day, coming home for 6, having dinner then it's pretty much bed/bath time, or homework sometimes.
His mum got back in touch when he was 6 and ended up fighting for custody which she didn't win, but she got weekend contact. So every weekend bar one in four he's at his mum's. Every evening he's at his grandparents'. There was a lot of bitterness caused by DP's willingness to agree to this contact. She was told by the courts she could go for one weekend a month to start with, but DP was adamant he wasn't doing that, as his mum would remain a stranger, and for DSS's sake he wanted him to have a good relationship with her. He regrets offering three weekends a month but is glad he was able to get to know his mum and her side of the family.
Somewhere along the way, everyone overcompensated for the shitty situation by spoiling him and never asking him to lift a finger. It's a poor choice but I can see how it happened.
But DP was single for years with one girlfriend in between for a while, DSS wasn't really at home to learn to do anything, the poor kid got passed from pillar to post - but other than leave his job and sign on, DP had no other choice. He didn't plan to be a single dad (not that anyone plans it!) and certainly didn't expect her to leave completely for 5 years.
Then, 3 years ago, I moved in. So he started coming straight home after school, and because I'm a complete mug (and really wanted this situation to work!) I just did everything as it was easier than nagging. But it wears you down over time, and then I realised I was very much part of the cause of the issue we've ended up with. I don't have kids, I was thrown in the deep end with a 14yo lad who's VERY different than me at that age.
I feel like I've messed up so badly sometimes. I've not done him any favours at all, and now that I'm trying to change things it makes the atmosphere in the house crap. DP is super supportive but works full time and then some as a key worker so it's just a fact that it's me here all day - nothing we can do about it.
But I'm public enemy number one.
I think he's treated like a guest in everyone's house - which is really sad! But means he doesn't do anything, anywhere. Here is his legal home, but until I moved in he spent the least time here!
But I'm determined to change that for all our sakes. For my sanity, for DP and DSS's relationship, and for his own sake, so he knows for the first time what it's like to be a part of a family unit!
I feel like I spend a lot of time moaning about him, and he is a pain in the arse, but you know what, when things are good we get on well. I care about him and want him to do well. But I need to learn to stand up for myself and not be taken advantage of.
Sorry for the length!