As previously stated, 1 angel in a community tank should be fine. You do need to remember that Angels naturally eat neons in the wild and you might want to switch out for something larger such as lemon tetras or cardinal tetras. There is a golden rule for angels and tank size. For the first 20 gallons, 1 angelfish, then for every 10 you can add another one. Angels develop high fins and need a tank that is 18 inches tall, or their fins can be damaged by brushing against the rocks ect. Angels are almost impossible to sex, so buying 2 random ones is probably not going to work. If you do get a breeding pair they will torture your other fish and you need to usually raise the babies buy hand because angels have all but lost that ability. If you possess more than two, the strongest will beat up the weakest.
If you want to do a breeding pair a 20 gallon will work if that's all you intend to do is breed them. Keep in mind that angels are sensitive to water quality and require a mature, cycled tank before adding and don't handle poor water quality too well.