Personally I'm also tempted to leave them in the dark about everything so if everyone's ok with that, that'd be my preference.  

As for language, I know it's going to be inaccurate but if you don't mind, I'd keep the language modern English,  reason being that English isn't my mother tongue and I won't even pretend knowing anything but modern. So unless someone wants to teach me... xD

We can discuss the preferred century and all if you want.