When DSD quit college we were very clear that we were supportive of her decision but she had to be doing SOMETHING.
Between her parents and me, we took her to career fares, sent her job ads. The jobs didn't want her because she had no experience and she had no experience because she didn't have a job. So we helped her secure some decent volunteering opportunities which helped build her confidence and her CV with customer skills, and recognised training in first aid, food hygiene, safeguarding and more. This is what helped her get the job.
She had a grand plan to move in with friends aged 17 so we had to have a very clam grown up conversation outlining all of the financial responsibilities of a household and they finally realised it was pie in the sky.
Why am I saying all this when it's a different situation to yours? Um, I think I'm trying to show that even when it's hard to find a job (and it is hard at the moment), it's not hard to find SOMETHING, to find volunteering or community groups or something constructive to do with your day.
That's where your son has cocked up and he's responsible for his life decisions.
Our kids are told that they don't have to follow a set path set by us but they do have to at the very least be on a path.
19 is hard. At 19 there will be people mid uni, working abroad, travelling, getting through professional exams, in the armed forces, training, all sorts. When my DSD was 19 she had a bit of a wobble but we all helped her recognise that she's doing well, she loves her job, it's in the right direction for the long term career she wants, she's earning enough money to pay for travelling with friends and having cool experiences.
I am very concerned that you felt the need to hide knives. Very concerned. I understand that he didn't try to be physically violent but that your mind would even go there terrifies me as it suggests such a high level of danger from him.
How old's his little brother?