Delete the "of the"
They are two rare people, who believe in ...
and it references both "rare people" and "they", which have been equated by "is" and thus are referenced equivalently.
Inserting "of the" does not change much about that.
Whereas the prediction, that "who ..." were not referencing "people", would be atypical and leave the kind of "rare people" underspecified. Placement matters and the immediate situation of "people" and "who" next to each other invariably determines the scope of the surface form. However, the subordinating "of the" is merely supposed to disambiguate that it's the kind of people, not the two persons per se, what is rare.