Yeah... They don't get pregnat X2.
The female will always have eggs.. lots of eggs. Those eggs need to be released, fertilised, and they need to hatch before there are any babies.
Hatching takes a certain temperature, it takes a daddy tending the eggs to keep them free of fungus, it takes still water so the eggs don't get sucked into a filter, it usually takes quite a number of eggs to produce half as many viable fry, and still many fry die of varous causes in the first few days of life.. including their bigger siblings eating them too.
Bettas are strictly carnivores... meaning meat. They eat creatures they would find in the water in the wild... mosquito larvae, freshwater shrimps, other kinds of fish fry (babies), other small freshwater organisms.
Just close your eyes and imagine a rice paddy or canal or river in Thailand... You're under the water, ok... Where would the fish find hay (aka dried grass) to eat?
Anyway... they weren't meant to eat vegetation... they were meant to eat other creatures, period. The fry (babies) especially need their diet to include creatures that are living.
Thus, neither of your fish would have much trouble gobbling up their own young. The daddies protective instinct sometimes doesen't kick in until they have a large group of eggs going, sometimes until their second or third spawn attempt. And if all the eggs got lost in the gravel, as they can and will do, he wouldn't be able to find them to protect them at all.
Sorry if that's not what you wanted to hear