The reason
Eric and
Colin seem "feminine" to you is that in the Hawaiian language there is a rule that
every word must end in a vowel sound. The Hawaiian versions of
Corbin and
Gavin, Kolupine and Kawine, would have the "e" at the end pronounced; it would not be silent and so they would sound something like "ko-lu-pee-neh" and "ga-wee-neh". (I'm not sure where the accent would fall.)