What sort of dimensions is it? I have a school of 6 mature ones which I think is minimum in a 4ft x 2ft x 2.5ft. Also have 6 young ones. Mine are skittish and need room to move. About 3 and a bit inches long in length. Hopefully the younger ones will be less flighty.
I have 5 angelfish in there and find if one or two mark out an area then about 1 ft by 1 ft will get taken up. So I have had one or two at one end of tank, the rest at other end and the tetras floating around in the middle. Having a high, planted tank has helped but it's pretty full. So all depends how your angelfish get along. Might be best to have one as a centre display fish and increase the school of your tetras. The male congo tetras have fantastic colours once they get above 2 or so inches.