These fishes are commonly found under ledges and in caves, and at night. Their bright red coloration looks dark at depth, where all the red has been filtered out of the sunlight.
Squirrelfishes
Bluestripe Squirrelfish
Sargocentron tiere
(1: First Cathedral, Lanai / 2: Tortugas, Kauai)
Crown Squirrelfish
Sargocentron diadema
(1: Shark Fin, Lanai / 2: Menpachi Caves, Lanai
Crown squirrelfish have black on their dorsal fins; Hawaiian squirrelfish don't.
Hawaiian Squirrelfish
Sargocentron xantherythrum
(1-2: Shark Fin, Lanai / 3-4: Three Fingers, Kauai / 5: Mario World, Oahu / 6: Koko Craters, Oahu / 7: Amber's Arches, Kauai)
Longjaw Squirrelfish
Sargocentron spiniferum
(1: Inner Crater, Molokini / 2: Second Cathedral, Lanai)
In the second photo, it's the larger red fish.
Spotfin Squirrelfish
Neoniphon sammara
(1: Pawai, Kona / 2-3,5: Garden Eel Cove, Kona / 4: Pentagon, Kona / 6: Dog Beach, Kona)
Soldierfishes
Bigscale Soldierfish
Myripristis berndti
(1: Shark Fin, Lanai / 2: Menpachi Caves, Lanai / 3: Kaloko Arches, Kona / 4: Brennecke's Ledge, Kauai / 5: Garden Eel Cove, Kona / 6: Camp One, Kauai / 7: Dog Beach, Kona)
In the 5th picture, the lower fish is a pearly soldierfish; note the shorter jaw and finer scales compared to the bigscale soldierfish.
Brick Soldierfish
Myripristis amaena
(1: First Cathedral, Lanai / 2: Pentagon, Kona)
Brick soldierfish have all red tailfins (no white). Note that the middle fish in the 1st photo is a pearly soldierfish; it's common to find multiple soldierfish species hanging out together. Similarly, the 2nd photo has a brick soldierfish in the middle, surrounded by pearly soldierfish.
Pearly Soldierfish
Myripristis kuntee
(1: Reef's End, Molokini / 2-5: Garden Eel Cove, Kona / 6: Corsair, Oahu / 7: Dog Beach, Kona / 8: Turtle Heaven, Kona)
Yellowfin Soldierfish
Myripristis chryseres
(1: No-Name Paradise, Lanai)