On all my playthroughs, I've entered through his office/bedroom and used the doorway as a chokepoint. I sneak a character up to where I can teleport him into the room, focus him down, then deal with everyone else as they enter.
Heh, you can do that even more cheesy! In his private chambers there's a Rivellon globe. Use telekinesis to move it near the door. Unchain your telekinesis party member, run into the main hall and initiate combat. Run back into his chamber and place the globe in the door – its collision box will prevent the foes from entering. As the globe can not be destroyed, the magisters won't be able to force their way through it. But the globe does neither (fully) block projectiles nor line of sight, so you can attack the magisters with ranged attacks and Orivand can use Phoenix Dive to get into the chamber, where he's seperated and can be taken down easily. When that's done, run off and regenerate if necessary. Then, when you're ready again, move the globe out of the door and deal with the magisters and silent monk.
#NerfTelekinesis
