All the fish shoud get fed variety of food, especially salt water fish. Rather than feeding one or two varieties, try using as many different food as possible. Ther are many dried and frozen food avail and among those there should be food specifically formulated for angels (not that these are complete diet for them). Well, at least I had medium freezer dedicated to store pretty much all the foods avail on the market and Homemade food.
I believe longevity of fish in captivity depends on water quality, foods and their ability to socilaize (compatabilty, lol)and size of tank.
Uless tank is very matured Reef, tank may not have/grow enough of proper algae for angels to graze and sustain themselves.There are many hobbyist who uses concept of
refugium to grow algae (Macros) to be used as food and these algae will keep the water in check in return
Always included bits of Green Seaweed (NORI) from Asian Supermarket (lot cheaper than one from
LFS) in non reef tank with angels and tangs and other grazers.