Depends on the angel, for some, like the Flagfin, Majestic, Clarion, Singapore, Asfur, etc require a minimum of a 75 gallon tank, preferably somewhere near 100 gallons. The larger ones, such as the French, Queen, Emperor, etc, need at LEAST a 150, bare minimum, preferably 180+. For that pair of regals, since they only get about 8" full size, I'd say for the two of them, they'd be comfortable in a 150.
~Adam