I guess I can divulge now that Geb's name is actually from the egyptian god of earth
Malvenicus is pseudolatin. From "Mal" = Bad and "Veni" = I came. Roughly combining (with a total disregard for the rules of latin grammar) into "the evil that came" (yeah, he doesn't know any latin either). Meant to sound somewhat vaguely threatening (tho he regrets that now).
King Nebra of the Dwarves was named after frequent commenter/reader Nebra Repalk.
Rhyme is a nickname, given for obvious reasons.