I know several angelfish breeders that keep young angelfish pairs in a 10 gallon. But i don't recommend that, i'm just stating it can be done and without illfull effects.
Most angelfish breeders recommend at least a 20 gallon tank for angelfish. I got a 20 with 2 grown angels and everything is going great. They got plenty of space to swim around and so forth. I also got a 29 which is the same height but bigger. Now i do realize some angelfish do need a very high tank such as the veiltails but other angelfish probably do not.
As long as you give each angelfish 10 gallons of space and its at least a 20 gallon with no veiltail angelfish, your doing fine.
Now angelfish tankmates can be the large tetras (cardinals are big and look almost like neons, if you wanted neons), rams, corys and most friendly slow moving fish. But beware that once your angelfish grow about 6-12 months that when they reach sexual maturity that they will be very aggresive towards your other fish. Some fish can handle it like my rainbow but many fish it might stress out to much and you will have to seperate the 2 angelfish into their own tank.