顔の見えない誰かに...
I wonder how this is translated as '(to) someone that cannot see their faces'. I thought at first that 見えない誰か, as a modified noun, is connected to 顔 with の to mean 'someone that cannot see of faces', which is weird...
I have never seen this pattern before and my research ends to no avail.
In relative clauses の is frequently used to mark the subject of the clause in lieu of using が.
So, as a stand-alone sentence, the clause would just be.
顔が見えない。-> I cannot see their face.
But then the が becomes の when used as a relative clause.
顔の見えない誰か -> Someone whose face I cannot see
There are various restrictions on when this can and cannot be done. One such circumstance when が cannot be substituted like this is when there is both an object marked by を and a subject in the relative clause.
