Sexing Jewels

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Can anyone help me sex my Jewel Cichlids please. I bought 13 in total from a breeder close to me. I am hoping for a pair out of them and to sell the rest on. The biggest is around 2" now and the smallest probably an inch. I can't particularly tell any difference between them at the moment and was wondering if anyone could give me some advice. They're starting to show their colour now, they are the blood red type so will make for stunning fish when adult. I know they can be extremely aggressive, but the guy i bought they from had them in with mollies, humbug cats and the pair of HRP's that i also bought from him and they just kept themselves to themselves even though they were brooding a batch of eggs.

Any help would be greatly appreciated.

Thanks.