The known members of the Tequila Mockingbirds include future Bart Simpson (guitar and vocals) and future Ralph Wiggum (drums). Little is known if there were original members who left as these are the only two shown.
Creation and Ending
Nothing is known about the creation of the Tequila Mockingbirds' creation, however, the band is ended abruptly in the episode "Bart to the Future". After they preform for Nelson Muntz for a wage of drinks and are booed of stage, Ralph decides to pack in working for the band. Seeing no alternatives, Bart gives up as well, ending the band forever.