Son so stressed all the time. How can I help?

What he needs to do and what he is prepared to do is another thing.
From my own experience and friends with adult children advice from parents isn't always taken well.
Does he have a friend or someone outside the immediate family circle who he would be more prepared to take advice or suggestions from.
If he asked for advice that is a different thing.
What I would do in your circumstances is play a supporting role for the whole family.
The children especially, could you have them to yours, put some routine and pleasure into the day with you and something they will look forward too.
Do you have a relationship with your DIL?
As ordinary people we can only show our love and support for our families as they come up against life's trials and let them know we are there for them.
We still worry about our children even when they do become adults it's only natural.

I really appreciate all the wise words. Not sure I can get him to go to GP but he does need stress management techniques. He had a serious head injury in his teens and we were not sure how this would impact on his future. He has done adult mile stones, job, relationship, kids but really struggles especially as relationship is not supportive. His head injury may not be a factor difficult to say as his life style is not an easy one and he hasn’t always made the best choices. Difficult t watch all this playing out.

He needs to get professional help. First port of call should be the GP. He may need medication in the short term. He certainly needs anger management. Feel sorry for the family, but unless your son is prepared to change then these problems will be passing into the next generation. Maybe already has. But that's not to say that the situation can't be made better with good will and motivation. I wonder about your son's childhood too, how these issues got a hold?

There are a lot of problems to be dealt with there Struthruth Counselling is a good start, it could also benefit the young carer to have input from a support group.
All you can do is support them and give the children a calm stress free place to go to.
I hope things improve for your son and his family.

Oh dear it may not go down well as men have an inbuilt fear of asking for help but somehow your son has to be encouraged to seek some professional help with his inability to manage life’s up apps and downs without anger
Anger is usually a way of managing panic and anxiety and his home life is in turmoil and for the sake of his children as well as his own he urgently needs to get help
I m glad to hear they are having couple counselling and the fact that he is willing to participate in that is a good sign I hope they will seek some professional advise for the youngest child whose behaviour may well be learned from his Dad
I am sorry that your 13 year old is a carer for his mum I always think this role is so unfair on a young teen
Encourage you son to get anger and anxiety management and do what you can for the grandkids that’s really all you can do Good luck