http://www.behindthename.com/php/extra.php?extra=r&terms=elwynThis site sais Elwyn is derived from Elwin and that is derived from the old English name Ælfwine. Alvin is derived from Ælfwine as well.
Alvena, Alvina, Elvina and Vena are derived from Alvin, but I think you can see them as female versions of Elwyn as well (since they are all derived from Ælfwine).