If they are young you could go with a ten gallon but 20 is considered a minimum.
Quick Stats from live aquaria
Minimum Tank Size: 20 gallons
Care Level: Moderate
Tank Conditions: 72-78°F; sg 1.020-1.025; pH 8.1-8.4; dKH 8-12
Max. Size In Aquarium: Up to 3"
Color Form: Black, Orange, White
Temperament: Semi-aggressive
Reef Compatible: Yes
Diet: Omnivore
Compatibility: View Chart
Origin: Papua New Guinea, Solomon Islands
Family: Pomacentridae