disable HMD devices when engine starts.
check my answer at: https://answers.unrealengine.com/questions/592480/run-two-game-instance-on-one-computer.html?childToView=917387#answer-917387
no need to restart the editor, still can use SteamVR plugin content and no need to have visual studio to build game 
(you need visual studio if you change the default set of plugins)