The Blue Brothers are a duo of 18-year-old pop singers in Liberty City consisting of twin brothers Billy and Bobby Blue. They are featured in The Ballad of Gay Tony where Luis Lopez is requested to pick them up from the MeTV building and drive to Maisonette 9, whilst being chased by obsessed female fans. Luis states that he is only helping them out because his niece is a fan of theirs. Despite wearing promise rings, they still have sex with their female fans. They never swear, instead spelling out their curse words with asterisks replacing some of the letters (saying "fuck" and "bitch" as "F star star K" and "B star star C H" respectively). One of the brothers, Bobby, took pictures of himself dressed in women's lingerie and accidentally sent it to nearly a half-million fans over Bleeter.
Their youth, refusal to explicitly use bad language, 'promise rings' and popularity with young girls strongly suggest they are a parody of the Jonas Brothers, while their name is a reference to the Blues Brothers.
Billy is voiced by Daniel Tay and Bobby is voiced by Harrison Chad.