Anya, I can only confirm Julia's answer: "one of ...." does have a literal translation in Russian:) As about "ты наш(а)" - well, it can have this meaning. It does _make_sense_, and I even think I could have used it this way. I disagree here with Julia... partly at least. Normally the context is strong enough to rule out the 'wrong' meaning and 'possession' and 'affinity' aren't actually too different ('my brother'), especially when the possessed is a member of 'possessor' ('we'). But it is not really common and not really idiomatic. Without the context Julia's meaning comes first to mind, that's why she objects. Moreover, this meaning of 'possession' (though in a good way) will always be somewhere around.

literally ты один из нас - it works as well , but at more colloquial way - ты тебя знаем ( meaning we trust you ), ты свой ( you belong to our community )

If you want to use the word "наш" it would be more appropriate to say in such cases "Ты - наш человек"

"Ты наш" or "ты наша" shows a possession and such expressions have meaning "we own you/ we got you" In that case we use the same construction like in English "ты один/одна из нас".

или "Ты - один из нас"