Hey ,
I do not see this asked in the post but what does the SteamVR overlay show you? Does it show you everything being all green or is everything all grey? Do you even have SteamVR enabled? If not you will need to download it from the Steam Client, install it, and then run it as SteamVR requires that you install and run the SteamVR tools or you will not be able to get the or Motion Controllers to work with UE4. Below is an image of what the SteamVR overlay should look like.
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Please note that since I currently do not have my setup mine is all greyed out but when working, the above icons should be all green. Please let us know if this helps or not and if not we can try a few other things.