You can have two copies of WoW open, no problem. As Blizzard has already stated, any software OR hardware that broadcasts inputs to multiple clients is forbidden. So as long as you’re manually alt-tabbing between them to input commands to the unique game clients, you’re fine. The second any automation is detected, like using some kind of macro script to rapidly alt tab between them and repeat the command, you’re going to likely get flagged and permabanned.