You shouldn't simply have 2 bettas in a tank. To do a betta sorority it's best to get a minimum of 5 and heavily plant your tank. A sorority can sometimes work and sometimes fail so you should do a lot of research before committing to it, you should also have a separation plan if things don't work out. Female bettas CAN flare but it's smaller. I can't help much with identifying the gender though he/she looks like a female to me.
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