Thank you for submitting your question.
First of all, given his medical history, a medical cause of his aggression should be ruled out( e.g. worsening kidney function can cause agitation).
He is on very low dose of xanax. Xanax has a calming effect. You should first consult with his regular doctor, but I do think giving him 0.5mg of xanax when he starts to get agitated can be helpful. This can be done every 6 hours, but do not dose more frequently than every 6 hours, and limit to less than 2mg in 24 hours( this means in addition to his regular scheduled xanax, you can give 2 additional doses as needed to calm him down).
There are no drug interaction between these 2 medicines. However, thorazine is rarely used these days( it is an old style antipsychotic with many side effects). You may want to discuss with his physician re: trying the newer antipsychotics like zyprexa. Another question for his doctor is whether he truly needs both buspar and prozac( both are antidepressants).