just you and him, ask about his day, how he is feeling, what he needs, etc.. No distraction by the younger ones, or anything else. Let him know that you are always there for him.
Emphasize to him that he is to be a sovereign individual in seven years. He needs to learn to be responsible for himself. Parents are very proud of him and here to help him now, but not forever.
Whenever he shows frustration, ask him not to feel but think. Give him all the time he needs and stay quiet (i.e., do not show your own anxiety) until he does. Tell him that his "lizzard" brain wants to run away, but he should use his "man" brain to stand and fight. Ask him to focus his energy on a solution (e.g., "Do you have a lock that I can borrow for today's gym?")
Tell him that he is worthy of his effort because he is free, which requires him to think and not dwell on feelings.
