At least one of these should be okay, depending on the age, maturity and squeamishness of your nephews. I wouldn’t have found any of these nightmare inducing as a kid. The poor dog in Old Yeller filled that role.
The Little Vampire Cutesy, but really fun. Pretend vampire meets real ones. How old are the boys? Would they enjoy flying vampire cows that launch a cow pie assault?
Killer Klowns from Outer Space Not for those with a clown or circus phobia, some older teen sex humor, person used as a ventriloquist’s dummy, some swearing
The Lost Boys Vampires, cheesey 80’s clothes, one implied sex scene, lots of vampire deaths, fewer human (mainly offscreen), limited swearing
These I would limit to 13 or older:
Near Dark Vampires in the desert, no sex, quite a bit of swearing, much blood in one truly horrific scene (one of my favorite movies)
Dog Soldiers Werewolves, guts (literally), gore, swearing, the son of Dr. Who, no sex
Blade Vampires, campy, blood, gore, swearing, much fun