I agree that boys are beautiful, with their long fins and bright colors. But females are also beautiful! Keeping three boys in a divided tank would be OK.
A sorority is very difficult at first. I don't know you so I can't say if I would reccomend it for you or not. You need to be able to make quick decisions on when the female fighting becomes too much, how to treat the rips in the fins, judge who alpha is etc.
I have a sorority, and it was very difficult. Not just from the above mentioned, but from the stress of worrying about the fighting between the girls.
Do you have female bettas now? Although they aren't that much different from males, maybe you should get some experience with a female betta before leaping into a sorority. I had two females for about three months before I started my sorority.
If you do decide a sorority, you need to do a lot of research, and ensure you have a big enough tank. You need at least a 10 gallon, but the bigger the better.