It sounds like you might have a pair, but they are still quite small. You won't be certain until you see mating behaviors/a female guarding eggs.
As far as food, I was only ever successful getting them to accept ghost shrimp. It's good that they are enriched. They should be each time they are fed out. I don't know where you sourced them from, but you can try different foods and see. I wouldn't try live brine though. As far as amounts, you should keep offering food until they are full, 2-3x a day. They will eat more as they get bigger. Females, at least in my experience, were bigger than the males if that helps you any. But you could also have the same gender and one is just more competitive. It'll likely be a wait and see scenario. They do tend to be the same size for a while.
Here is an article you can use. It helped me a lot. It's a compilation of different articles, but it discusses Flamboyants as well. Brett pioneered the husbandry for these guys and has a lot of great information in there about them.
http://drumandcroaker.org/pdf/2014.pdf
Good luck with them and please reach out if you have any more questions. They are a very challenging species but incredibly rewarding as well.