My sympathy JaniP, you are in a frightening situation. Your GS clearly has anger management and behaviour problems because he has already caused his parents problems. The reason for this is irrelevant. You are dealing with how he his behaving now
The first thing to do is get in touch with an elder abuse group. They will be able to help and advise you on every aspect of protecting yourself. They will also be able to provide a listening ear and assistance.
The second thing you must do is make sure your house is secure. If he has a key,then change the locks. Make sure the front door has a chain on it so that you can talk to a caller without being in fear of them pushing the door open and coming in. Make sure your windows all have window locks and that there is a good bright light outide the front door.
If he does approach you keep a diary of when he visited, how long he was at the house (do not let him in) and what he said. Note, also, any other approaches, save emails, note phone calls as above and save any texts. Do not intiate any contact with him yourself.
Talk to other members of your family about the problem. Ask for help and advice.
And while we all love our children/DGC and DGGC, constantly giving them money whenever they spin a convincing story is not always a wise thing to do. They begin to see you as a money tap, a sort of get-out-of-gaol card whenever they mismanag their affairs. Eventually they turn nasty when you have to say 'no', the money has run out. This is how he sees you now, as a cash cow to be milked as often as possible.
So keep your money and let them solve their own problems. I bet your GC lost his job because he lost his temper with his FiL or for some other misdemeanour. Behaviour that should not be rewarded by you givinghim money to help him until he got another job.. As somone said in a similar situation. a short course of starvation, might do him good. His wife and child would, I am sure be supported by her parents.