Congrats on your fish, looks like a nice little group. They are burundi and you said one has 6 stripe on one side and 7 on the other. When stripes are messed up its usually due to bad genetics and inbreeding. If you have plans for breeding them, I would exclude this one from those plans. As for sexing them the best way to tell will be to vent them. They will probably lip lock and nip at eachother but that's about it, they are pretty docile fish. As long as their tank mates are not aggressive you should be fine. They do grow slow I have had some reach 5-6 inches in a year span while others took longer. Good luck!