"We have decided to follow this last street."
Translation:Abbiamo deciso di seguire quest'ultima strada.
The correct way to write it in this case is to add the adjective ultima before strada, "quest'ultima strada." It actually sounds funny to me when it's written "questa strada ultima." Nevertheless, adjectives normally do not go before the noun, except if it is a "passive sentence" or "passive noun", something like that, I don't really remember that well. I hope there is someone who can explain it better;P