Relationship between go! Express and Mokulele?
From Mokulele's FAQ page:
When flights are full, Mokulele Airlines and go! Express reserves the right to stow Carry-On Baggage in the cargo compartment of the aircraft. Carry-on baggage may be limited further by aircraft type or storage availability.
go! Express operates the Cessna Grand Caravan on routes to or from KOA or OGG, JHM and HNL. Your checked in baggage should be no more than 45 linear inches, or 9"x14"x22" (L+W+H), and weight no more than 50 pounds.
Codeshare?
Mokulele now offering o/w flights starting at $45.