yeah, lol - "Mario" are their last names. Surpising how few realize that, but it's "Mario Bros." just like "the Wright Bros.". Their last names are "Mario", and for some sick reason one of them also has it for his first name
Hence: Mario Mario and Luigi Mario.
EDIT: Added a link about Mario Mario's history of games for "justification" lol.
http://www.retro-games.co.uk/classic...s_me_mario.htm