OK, I read back over you posts and have a few questions. You don't have to answer any or all of them, they are just things to think about.
You said your BF parents are sick, how sick? Are they on disability? Are they elderly, or of an age where they could reasonably be expected to take care of themselves? Are they expected to improve, or is it something chronic? Are both of them equally ill? If you go on to marry this guy, will you be happy if he is spending a lot of his time/energy/money supporting his parents and not you? Please think long and hard about what you are happy to do.
I'm very glad to hear he isn't involved in drugs or heavy drinking, that would make a difficult situation hopeless, in my opinion.
I know he is depressed over his sisters death last year, but he was unemployed for a while before that, right? Where are her childrens father? Who is the legal guardian of the children? If his parents are too ill to look after the children, are you willing to take them on? Has he any other siblings?
He has told me that he sees a future for the two of us, and he knows he has to find a job, or at the very least, do a course to get him started.
What exactly does he see as his future with you? Ask him detailed questions, try not to say what you want yourself and try to find out what he wants. It sounds like he is telling you what you want to hear, with no real motivation to do anything.
Can I suggest that you start telling your friends the truth, instead of lying? It’s really none of their business if he works or not.
Is he open to doing some kind of counselling to help him overcome his feelings of low self worth and depression? While these are a problem, I’m not sure that anything else will work, IYKWIM.
Have you asked yourself, what will you do if nothing changes? If he can’t, or won’t change, can you live with him like this?