There have actually been four Nighthawks. Squadron Supreme Kyle Richmond. He died and his ward took over for him as the new Squadron Supreme Nighthawk. 616 Squadron Sinister/Defenders Nighthawk and then the reimagined Supreme Power Nighthawk.
Darkhawk is another character entirely. He was a New Warrior, had a solo series and is now a member of Excelsior in Runaways.
Golden Age Marvel (and other companies) was peppered with Batman type figures--though they took more from the Shadow and other pulp/noir/radio heroes like him. Batman was just the inspiration to dress those characters up in costumes. The Challenger exquisitely mimics Batman--his parents killed, he travels the world learning the skills to defeat evil-doers, although his story was a bit more layered than the original Batman origin.