The addon Jamba allows the slave to mimic the npc choices of the master.

So target the npc with the master.
Have the slave assist the master.
Hit your Interact With Target keybind.
Have your master do whatever.
And the slave will do the same.

This works for quests (starting and completing), although you can configure the slave to copy the masters reward choice or for the slave to need you to pick from their screen, also works for dialogue you have to listen to, vendors or flight paths.

A very highly recommended addon.



With two priests, I'd spec them both Shadow.
Holy/Disc can do ok damage too, but I'd feel Shadow will level faster.
Not sure the end-game goals, might want to decide their final specs when you get there.

For the most part, you'll just use Follow for movement.
You don't really need independent movement keys on the main.
Once you've broken follow via the back arrow key, the main can mouse move freely on their own.