They nerfed swarming mobs like the skeletons and spiders. COTA XP isn't that great any longer. If you play the game like normal, but on Torment VI (start the game with the level 1 and it will be Torment VI (1)), by the time you reach the Skeleton Kings Keep, level 3/4, you will be in your 40s. Doesn't take long at all. I've been using the Cain set for additional 30% XP with a 29% Ruby in the head socket. Then start the game over at the first quest and by the time you reach Legacy of Cain, you will be close to 55. You can then mix up COTA and then Leoric Keep 3-4 runs a few times to get to 60. Most of the time I have my guys stacked ontop. What kills them are range. I'm using Slow Time on the mages, with one configured with Point of No Return rune. Helps to keep things at bay and slowing down projectiles.

As for controlling 2 windows, look at the activate Repeat and Mouse Repeat Mapped Keys in D3-Always On. That disables/enables it on all windows. I'm sure if you made a copy of it played around with the settings, you can configure it to disable the mouse broadcast on 2 specific windows and keep the mouse broadcast active on the Mage windows. You'd still want the default broadcast to all windows mapped, so you can move everyone at once.