What you describe in your brother does sound like some sort of seizure-like activity. This is probably due to some post-trauma injury, especially in light of the former grand mal seizures. Stress and frustration can often trigger partial seizures, which is what these sound like.
Is your brother being followed by a neurologist currently? There could be some metabolic problem either causing this or aggravating it, but over the course of 20 years and having begun after an auto accident, a metabolic problem would likely have progressed long before now.
Your brother definitely needs a neurologic consult to at least establish a baseline record, and probably would benefit from some sort of medication to help relieve the seizure activity.
I hope this is helpful to you. A more definite diagnosis can only be made (and a treatment plan begun) by a neurologist. Please keep us updated.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist