Translation:Where will the bottles of wine be kept?
Well, the original sentence is passive, so there's nothing to tell you it's "they". I could be speaking about my own bottles.
Yes, suspect; but unfortunately there isn't always a clear indicator :) An auxiliary that clearly implies the passive is venire: "dove verranno tenute le bottiglie di vino?".
I wrote "where will the bottles of wine have been kept?" Is that not right because there was no avranno? Confusing!