Hello,
Sexing angels is extremely difficult to be %100 accurate. Some males can develop a larger forehead bump, and females a little flatter from mouth to dorsal fin. This isn’t a certain way though. In the past the faster growing aggressive angels, in the tanks I have, turned to be male but not every time. The only way to know for sure is when they are actively breeding and can see there breeding tubes. Males are pointy females are rounded. The best bet to get a pair is keep them all together, keeping water quality high. They can figure out the sexing part themselves. Start to pair around 12 months but I’ve seen 10 months and also 2 years ? to get a pair. Good luck