Statement (1) is true: Mangal Pandey was executed in April 1857 for his actions at Barrackpore in March 1857, which occurred before the widespread revolt began in Meerut in May 1857. Thus, he is considered a martyr who inspired the subsequent revolt. Statement (3) is true: Kunwar Singh of Jagdishpur was a key leader and organizer of the revolt in the Bihar region.