yes...please dont let any of them house together... surprisingly, females can be even more aggressive then males.
also, it's a misconception that bettas can be put into bowls and not change their water because they live in rice paddies in the native.... although the rice paddies is true. it is not true they can live in tiny bowls!. rice paddies belong to a LARGE collective unit of water...bowls do not. bettas, just like any fish, gets very stress with ANY anonmia in their water...and the tiny bowls, this poison builds up too quickly!!!
you can look for stress bars on them...
ideal is at LEAST a gallon, and 100% water change can vary between bettas and how much amonia they produce. test for amonia every day, and as soon as any trace shows up, you know that water change is the day before. usually it's every 2-5 days with a gallon of water.
also, tiny bowls can not be safely heated. bettas are tropical fishes that requires temperature around 78 degrees. any cooler and they become lethargic and simply "float" there.
Trust me...add the heat and they become very energetic!!
They also like places to hide... anything will do...even a very CLEAN mug placed on its side will do...or simply get those pothos plants snip off some vines and voila....their own jungle that they can hide and play in!!
in terms of food...it's very important NOT to feed dried pellets and more importantly freeze dried!!!! it will give them bladder problems and may permently cause their glands they need to stay bouancy to be damaged.
There are tons of alternative...and when feeding tiime comes...you can literally hand feed them! Even at PetSmart, they have a "refridgerated" section with frozen blood worm, shrimp brine, etc. Blood worms are GREAT for them as Bettas are Carniverous!!! (not herbivores like those marketing and stores convey when they stick them in a vase with a plant!!!)
They only need about 2 worms a day!! And you can simply take a toothpick, hang a worm off of it...and dangle it in front of the betta!!
The other alternative...and the best and healthiest is live feeding.... Look at PetSmart...they'll have a container, usually in the reptile section, that have FFF, or flightless fruit flies. Gross I know...but pop one into the tanks...and watch the betta go wild! This is closer to their natural diet and instinct! From one of those tubes, you can make an endless supply of 'em...if you want to know how to breed them... just let me know... Theyre not that gross since they cant fly.
Also Dapnias are great too!! Theyre like water fleas... fun to watch and raise...and you should see how the bettas react! Dapnias are mostly escoskeletal (spelling) so easily digested.
Fasting them once a day a week is good for them.... It'll help them clear out their system...Feeding too much can do real harm! Fast for a day...and then give them a little piece of the inside of a pea....It's a natural laxative for fishes!
If you need more hints and tips..let me know...
I havent kept bettas in years.....but they are really awesome and filled with personality if kept properly.... water puppies if you will....