Ocellaris clownfish are among the more forgiving marine fish, but they still need a cycled saltwater tank, stable salinity, and marine-level testing. A 20-gallon tank can house a pair; 30 gallons is more comfortable.
Yellow tangs are active Hawaiian surgeonfish that need swimming room, not a nano reef. A home-aquarium minimum is about 125 gallons with length to patrol and rock to graze.