In the immediate term, you have to re-establish communication with him, and tell him whatever has happened in the past you are willing to work through it with him. Make it clear that he is welcome in the house if he is prepared to work with you to find a way to improve your relationship. Enlist the help of his sister to be in touch with him now to persuade him that things can be worked out.
If you really fear that he is at risk of harming himself, you can contact the local police who have powers of detention for observation should it prove that there is a real risk of harm.
It may well be that you son is suffering from depression, and is in urgent need of medical help, so you should be making that a priority. Admit that you over-reacted, and want to help.
When you do talk to him, there are some things you can do, and here are some tips:
What you can say that helps:
I'm here for you - you're not alone.
What causes these thoughts and feelings is a real illness, and it can be treated..
You may not believe it now, but someday, this will pass and you'll feel differently.
I care about you and want to help, even if I don't really understand what you are going through right now, how you feel, and what you're thinking
Don't ever give up - just hang on one more minute or hour - whatever you can.
You are important to me. Your life is important to me, and to everybody who knows you
I'd like you to tell me what I can do now to help you.
We can get through this together
Cheer up- it could be worse
Quit worrying about it - you'll be fine
Your just imagining it, it's all in your head.
Everybody feels like this sometimes
You'll just have to help yourself
I'd have thought you would be better by now.
Get over it and snap out of it.
Grow up and act like an adult.
What's the matter with you anyway?
You'll also find some helpful information here: http://www.familyaware.org/
In the longer term, you have to decide what standards of behaviour are acceptable, and which are not. Try to involve him in this process, because that way, ist is much more likely to succeed..
People like him are rather liable to push things to see what happens, and what they really need are firm boundaries. Being ‘soft' just makes you easier to manipulate, and anger just teaches them to be angry when they in turn are faced with a difficult situation.
These boundaries must include no violence, getting work, and commitment to play a part in maintaining the household .He needs to understand rights come with responsibilities, privileges, food shelter and money have to be earned.
In your situation, recent events within the family will (despite all you have done) have left him feeling a bit insecure, and he is going to need a lot of reassurance and support. Lots of praise for when he doe something right..
He is quite old enough to know about actions and consequences. We humans only indulge in behaviour that brings reward of some kind. Only when that reward (whatever it might be) disappears, or the consequences of our behaviour promise to be unpleasant do we consider changing what we do.
Here is the clue to sorting things out. When you are faced with non-co-operation - give him choices, and make sure he understands the consequences of his choice - and always follow through. If you don't he'll just get confused. Please make sure though that all his small successes are praised and occasionally rewarded. Consider what sanctions you might use - no mobile phone, no money, for example Privileges should be reinstated after he demonstrates that he has earned them by not crossing the boundaries you set.
When it does come to punishment, try to make sure that it is something that will have an impact "Look, you know you broke the rules, so you cook your own food and clean up afterwards this weekl." And make sure you vary it otherwise it becomes stale, and therefore more or less ignored.
Ask him too, what he is prepared to do to change his behaviour in future - tell him to research what might help him, what help he feels she needs, and even consider a ‘contract' between you. In other words, involve him in his own change, with a prospect of a small reward for success.
Never get angry, stay cool and in control, matter of fact and stick to the facts. Avoid drama.
Never, never be blaming or accusatory. Tell her how you feel about his behaviour, and make sure he understands that while you love him, his bad behaviour is hurtful and will not be accepted.
I'm going to suggest that you get a copy of the book "How to talk so teens will listen, and how to listen so teens will talk". Its ISBN is 13: 978 1 85340 857 1
Not only will it help you turn things around round it is also a good read!
Best wishes, NormanM