Westward Ho (1935)

Ballard's trail jumpers attack the Wyatt Company wagon train, killing young John's parents and kidnaping his brother, Jim. In post-Civil War California, John Wyatt, now a man, pulls together a vigilante posse, The Singing Riders, who all ride white horses, dress alike, and ride the trails singing and rounding up outlaw gangs. Meanwhile, John is ever on the lookout for the gang that murdered his parents As a youngster John Wyatt saw his parents killed and his brother kidnapped. On a wagon train heading West he meets his brother who is now a spy for the gang which originally did the dirty work. He and his brother both fall for Mary Gordon When Ballard and his men attack the Wyatt wagon train, they kill all except two young brothers. Twelve years later one brother John has organized a vigilante group. The other brother Jim is now part of Ballard's gang and the two are destined to meet again

Unfortunately the movie Westward Ho is not yet available on HBO Max.