After freeing Hendak, he thanks me alot and then proceeds to attack my party. We run into the Inn but he just keeps trying to kill us. What can I do?

You probably ending up hitting him accidentally with an area effect spell .I would restart the game talk to him go about killing all the guards then later letting him go and use no magic as i help him out.Watch him if he goes to red you hit him accidentally(the circle about him)