They are actually!
Rathalos, in Japanese is リオレウス (Liolaeus), so we got the idea to name him Leo. On the other hand, Rathian in Japanese is リオレイア (Lioleia), so we got the name Leia. A little inspiration also came from the Monster Hunter Stories franchise. We didn't want to make them too complicated of a name so we just settled for an homage instead.
I was wondering where the monster names came from.
I know Jin is Jinouga, Zinogre's Japanese name
I figured "Runan" came from "Ruiner", as in Ruiner Nergigante
Joseph wasn't hard to figure out. Deviljho-seph
Koku and Ridge I haven't got a clue
And I just guessed that Leo's name came from the zodiac sign Leo