hey ciro, it isnt that we dont liek to answer your questions or think that you pos to much, just you remind us of this kid who was always changing his mind about his tanks, no need to stop asking questions, i did this alot wheni was new to the hobby. besides, i always liek to answer questions,. as for your question, i dont think that there is any real solid way of finding out if they are male/female (i might be wrong), as for keeping them together, i dont think it is a good idea. first off, like racer said, they are very territorial and can easy kill each other if they decide to fight. as for keeping them in a 12 gallon, NO, very small for a such a nice fish. i would recommend at least a 29 gallon, but definately would prefer a 55. the only good small angel you could keep in your 12 would be a coral beuaty, i had one in my 15 before it died of old age. hope this helps