In an example sentence for the adjective "verschieden", I have
Die Geschwister sind sehr verschieden: der eine ist fröhlich, der andere sehr ruhig.
Now, as I understand it, both "der eine" and "der andere" should either be feminine singular accusative (carrying the gender of "Schwester") or should be neuter singular accusative (carrying the gender of "Geschwister"). Why then do we have "der eine", and not "die eine" or "das eine"?
Also, if this is in fact a mistake on the part of the dictionary, should it actually be "die" or "das", and why?