Jeff is the main guy followed by Ryan, but I'm sure i read somewhere they had a substantial financial backing, so that means Jeff maybe in charge of decisions and such but he may have to verify financial decisions with some other guy.
Yeah, Jeff and Ryan Co-founded it (and own it, for now) and there working with Whiskey Media to continue on improving the site. That is until, GB gets bought out by some big Internet network company in 4 or 5 years and then becomes huge.
Isn't it the interns who were behind the camera in the 'How to build a bomb' videos. I like their work area in the office and the motivational messages written on the walls in front of them by the other guys =D
As for who owns Giantbomb, you can click the "Whiskey Powered" link at the bottom of any page to learn more about Shelby Bonnie and friends. I don't know who technically owns the site, but they're paying the bills.
I think all four of them decide on things as a group, but don't count my word as fact because I'm just guessing. Now, as for who is in charge of the forums, I think Brad is. Again, not 100% sure. Just making some educated guesses.