You'd have to check whether your LFS might take them. I believe the big chain stores like Pets At Home don't take livebearer fry from home hobbyists, because of the threat of disease spreading, but my privately owned local fish store takes my livebearer fry. Whether they will would be up to the owner. If not, you'd need to look into selling or giving them away privately.
It's best practice where possible to separate them into male/female tanks as soon as they're old enough to sex, because otherwise the females can become gravid way too young, but it's not always possible, and anyone buying livebearer females should be aware that there's always a risk that they're already gravid or carrying sperm packets.
I wouldn't suggest trying to keep them all - your one female can pop out another 30-40 every month, then if any of the young females in this batch do get knocked up before you can separate them, those would be mature within three months and start popping out fry every month too, you'll soon be overrun with tanks and guppies!
But if you wanted to keep a couple of females so your own adult female isn't outnumbered by males, you could. Or you could rehome the adult female and keep a couple of the nicer males to have a male only tank if you want to avoid dealing with fry all the time. Up to you!