What are the full names of the men who harmonize with the guitarist?
Frank Fay, as a Mexican named Don Carlos, rides into a small Texas border settlement on the Fourth of July in the early 1880s. He is accompanied by his two inseparable companions, played by Georgie Stone and George Cooper. The day is being celebrated in the style of a  Spanish fiesta. Fay challenges a rough Texan, played by Noah Beery, to a duel, only to find himself invited to undertake the dangerous task of capturing a cattle rustler who has been stealing cattle from the Lazy Y Ranch. He accepts the task on the promise of receiving $7000 in gold if he can return both the thief and the stolen cattle within 10 days. 
During the next nine days, Fay spends his time making love to every pretty girl he meets, serenading many of them by singing the theme song to the film while playing his guitar, while his two companions join in the harmonizing. He lies to them all, telling each girl exactly what she wishes to hear. Throughout all this time, he does nothing towards earning his reward. On the 10th day, he captures the cattle rustler and turns up the cattle to everyone's surprise by using a simple method of which no one had thought. He rides back to Mexico with his latest conquest in his arms.
Georgie Stone George Cooper