Any fish fry are nutritious to all carnivorous or omnivorous species. Why should Betta fry be different?
after breeding the male betta might attack the female and the fry is in danger
No, she will eat them. The male should be removed as soon as the fry become free swimming - that's about two days after they hatch or four days after they are laid. Once you take out the male, start feeding the fry on vinegar eels and microworms. Any adult betta put in a tank with betta fry (even their own) will eat the fry.
You won't have any betta fry. The FEMALE betta is the one you remove right after spawning. The male stays in the fry tank until they're free-swimming.
Microworms
After spawning, a male Betta will kill the female if she is not removed almost immediately. He looks after and rears the fry by himself until they are free swimming. If he is not removed when the fry are at the 'free swimming' stage, he will eat the fry.
Brine shrimp.
First, when your betta has the fry, you must split them up quickly. But in your case, it looks like you didn't separate them. If you didn't, its pretty much hopeless. Just let your betta finish eating the fry. next time though, split them up quickly. Some pet stores usually have nets you can use to move the fry away from their parents.Unfortunatly, in your case, there really isn't much that you can do at this point. Right after the fry are born, you must separate the fry from its parents. So for now, just let the betta eat the rest of the fry. The next time you consider breeding more bettas, separate the fry from its parents quickly. Most pet stores have betta fry nets so you can scoop the fry away from the mother. i hope this works next time!
Female beta is a murderer.
The problem will not be the tetras coexisting with the Bettas. It will be the female Betta. She will undoubtedly be killed by the male. He may well spawn her first but afterwards, if she is left in his presence he will kill her. Also if he has ova or fry to look after he will kill the tetras in defence of his young.
Kill them you can fry an egg and break the yolk up and feed it to them
Male betta's are more colorful then female's