My step dad is 55 and has just had a massive heart attack yesterday. He is currently in a coma and has had to be resuscitated 15 times. The doctors are going to test him to see if he is brain dead, but he has had some jerking movements. Can you be brain dead and still have movement?
Yes, this is very common and a sign of severe irreversible brain damage.  It is called multifocal myoclonus