Paul Bettany could do a good Nicodemus (or Lord Raith). He has the natural look and the voice for either part.
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I would be more than happy with him as Nicodemus, but he's not Pretty or ageless enough for Papa Raith, plus Id want him to resemble Thomas if at all possible, which in my mind means looking like Matt Bomer
For me this is Clan Wraith:
Thomas = Matt Bomer

Papa Wraith = Rob Lowe

Lara and Sisters = Mary-Louise Parker, Kate Beckinsale, and Anna Silk (not sure which for lara, but probably Beckinsale for the range of scary personality)



The Twins (Madrigal and Madeline) = Ian Summerhalder and Parker Posey


Inari = Ellen Page

EDIT: Fixed the broken Mott Bomer pic