+1 to the advice given.
Bettas are aggressive and intelligent, therefore unpredictable. You may be able to get away with putting males and females together for a little while, but sooner or later all but one of them well end up dead......and that one will probably be so beat up that it will die shortly after. Its inevitable, they are called 'Fishing Fish' for a reason.
Even Sororities(groups of females)are risky and could end up the same way. All of a sudden they could just turn on one another. So if you want a Sorority, be sure to do your research, make the tank as densely planted as possible, add as many caves as you can, and get 4+ females in at LEAST a 10 gallon tank. Even then, watch then closely ALL the time....its still a big risk.
Probably the only way you MAY be able to keep males and females together would work is if you have a VERY densely planted 150+ gallon tank with a TON of cover. But, then again, thats STILL a huge risk.
Another option, however, is diving a tank....for four bettas, you could snag a 20 long and divide it into four sections, one for each betta. If you can only have a 10 gallon though, then you can only divide it into three sections...keep a male and one and the others for a female each. Just be sure the dividers are secure and keep the water level a couple inches from the top of the divider so they can't get to one another ;) Hope this helps some.