Bifur, Bofur and Bombur were descended from the Dwarves of Khazad-dûm, but not from the royal house. Note that the relative ages of these three Dwarves are never established, so this genealogical tree follows the name order preferred throughout The Hobbit.
Bombur's name appears to translate more precisely as 'tublike' or 'tubby'. There may also be a connection to bumba, 'drum', since a drum can also be seen as tublike, and was Bombur's instrument at the Unexpected Party at Bag End.