One way to avoid spew is to minimize contact. Make kid exchanges short and preferably at a distance (i.e. Stay in the car when dropping the kids off, or leaving immediately on his arrival if he's spending time with them at your place. ) train him to communicate with you by text, or better yet, email.
It's sad, and I know, scary that he's not getting the help for his PTSD/ tbi that he should. You've given it your best shot. If you think any of his family or friends would believe you, you can try passing that baton on to them . But ultimately, you may need to accept that you can't save him while he's focused on you as the problem. Drop the rope,
