I would prefer to translate "Invitiamo le vostre fidanzate?" to "Should we invite your fiancees?" as well.
Yes, the translation is wrong, and the pronunciation of fidanzate weird.
Edit: Nevermind, the sentence has changed and the translation is ok now.
I guess the sentence was fixed, I don't remember what it was anymore.
I wrote "let's invite your girl friends". It was marked wrong. I think it's correct, but can't be bothered to argue with Duolingo. "Andiamo" can mean "Let's go" (Let us go) and "Invitiamo" I think is the same.