A friend found out some very disturbing news and took 12 vistirals and 6 blood pressure pills. He will not allow us to call an ambulance. What should we do?

CALL 911. Your friend at risk and imminently in danger. Needs ed evaluation urgently. Call 911.
So what?! You should be a friend to him and call an ambulance immediately. That combination can be fatal and who knows what else he took or what else he will do. You should call 911 and tell them your friend is intentionally overdosing. They can take him by force to help him get treatment at the hospital.
Drug OD. Your friend has taken potentially lethal doses of medication and should be observed in a hospital. You should call the ambulance and insist that he go with them. He may pass out before they get there anyway from low blood pressure or the vistaril (hydroxyzine) dose.