If these are male Bettas they should never be kept in the same tank. Male Bettas (or 'Siamese Fighting Fish') are strongly territorial and won't tolerate the presence of another male. You can keep Bettas just about anywhere (a jar will do) since they're a labyrinth fish and can breathe air. Separate your Bettas.
You can put any other tropical fish that does not have long flowing fins or tail and is not aggresive.
Male betta's are larger, more colorful, and have much longer fins. Female betta's are small, less colorful, and have short stubby fins.
Your betta fish is a female if she has smaller fins than an average male.
Well there are lots of types of fins for betta fish. my betta fish has a long stringy tail and fins, but my female has short average fins. most have plain fins. mine is the only one i have seen in my area with a stringy tail. most fish have stringy tails if they are sick but not mine he was bred to be like that. depending on the fish and the area well there are lots of things that are considered normal for bettas.
Depends what fish you have, if the fish are colourful and have long fins then it'll probably bite it to death, every betta is different.
Well, betta arn't the smartest fish. It probably spreds its fins out because it "thknks" there is another male fish in their so it wants the female to pick him... Also I advise you don't put 2 male betta fish together because they will REALLY TEAR EACH OTHER APART!
There are so many different colour variations of Betta that red streaks in blue fins are quite common as are blue streaks in red fins. All it means is that the fish are cross bred.
Yes; fish fins can regrow and heal with amazing speed.
the size of it's fins and body
Just watch how they interact and if the betta is being aggressive isolate him. Bettas can be with other fish as long as the betta is a different color and there arent any fish with similar fins.
Betta fish get in fights with fish with colorful fins and bodies. If your betta gets in a fight while your away,the weaker fish may die. But if you see your betta fight with another fish you should try to split the two fish apart [or all the fish that are fighting].
No. all fish need fins to swim. Or they would just stay at the bottom of the tank and die.