Have some other people do groundwork with him. He needs to learn that he must respect everyone.
I think you need to work desensitization to the human. Desensitization does not require any particular equipment most of the time, it relies primarily on patience and repetition, as it may take several weeks to be effective. You can also ask another person to make an ethological diagnosis to find out where the problem comes from and why your horse reacts like that to others. The ethological diagnosis allows to evaluate the character of the horse and to take stock of the horse from the point of view of attention, confidence and respect.