As Tolak mentioned, you can't sex angels other than when they spawn. I've read that you can look at the bump on the head but that didn't work on mine. About the only way you can assure getting a pair is to buy at least 4. It's been a long time since I took a probability class but I believe just getting 2 angels only gives you a 50% chance of a male/female pair while getting 4 raises the likelyhood of at least one male and one female to something like 88%.