Flame Angels are dwarfs, so if the question is can you put one in, yes. 55 is a little smaller than recommended, but not that bad. Two in that size tank would not work. The Yellow Tang is a bad idea. They need much more room (most experienced aquarists suggest a 6' tank and the least I've seen online is 60-75g). I think that works for something like a Kole Tang or Tomini, but not a Yellow. The Kole or Tomini are usually fine in a 70+...I'm not sure about footprints between 55 and 75g off the top of my head, but I'm guessing it might be close enough.