Is my endler breeding plan feasible/humane?

Hello! I have a slightly unusual question today and would love some opinions/advice.

So I have 2 15g/56l planted tanks. One has 8 blue neon tetras and a honey gourami and the other has a betta (+both have shrimp and snails). About a week ago I got 5 male endler guppies for my community because they're funky little guys and I like them :)

Unfortunately there were also 4 fry in the bag... I put them with my Betta because I thought he'd enjoy a little snack. Well - he's old and turned out to not be interested in them at all. Okay I thought - 50% chance that the fry are male and I can put them with the others.

Welp, at least 3 of them turned out female (gravid spot + round anal fin) and now I have a couple of options.

1)bring them back to the store when they're grown

2)let them live with my Betta but only as long as he isn't too stressed out (so far he ignores them)

And I have an additional idea: I would like to witness a one time live-bearer birth experience 😅 so:

I'd put one male and one female into a separate container for a few hours or until they breed, put both back into their original tanks and then let the female have the babies. My betta might eat a few newborn fry since they'll be much smaller and the rest could grow up, I'd keep the males (separate them as soon as I can tell the genders) and give all females back to the store (my bf's dad works there so I can put them into one of their planted display tanks).

Is my plan okay to do? What do y'all think?

Thanks in advance 🤗