Platies, mollies, guppies, and sword tails are the four main live barrers you will find in any pet store.
Something few pet stores will tell you, (or even know) is that all four of these LOVE salt in the water. A lot more than most freshwater fish. In fact, mollies can live just fine in a MARINE tank! They are prone to a bunch of ailments without the salt. Shimmies, and clamp fin, just to name a few. Salt does wonders in preventing that.
All of these are native to the Amazon river and usually around the areas where it meets the ocean. That's why the salt. And they do all need heat. 78 would be ideal.
Can I assume the picture by your name is your tank? Those would be the common name of sunset gold wag platties. (Any with black tails and fins get the "wag" tacked on.) Some of the dark red platies you cannot see the young but yours might be clear enough in color to actually SEE the babies inside the mother. Just above her anal fin there is a dark cavity. Look close, you might be able to see some shinny eyeballs in there. Cool huh?
now.. getting babies from live bearers is no problem at all. RAISING them is a whole other ballgame.
First, the parents have absolutely no parenting skills at all. To them, it's just live food. They average some 20 or 30 young at a time, yet most people see five and figure their fish had babies. Well yea, they pigged out on most, the ones left are only after mom and dad are stuffed. Such is nature.
A very well planted tank, and well fed fish will help.
Breeders will sometimes use special holding tanks for pregnant fish which saves ALL the babies. But personally, I think the parent gets so freeked they expel the young too soon and you end up with a lot of dead ones. I'd rather go the well planted tank way. So a few get eaten. Most will be fine.
Baby fish will need clean conditions, they are babies after all, warmth, and food! FREQUANT SMALL feedings. This is where most people drop the ball. Fish eat all day long in the wild. They don't have a dinner bell. And cannot gorge once a day. but over feeding can polute the tank. So be careful here.
Now as for how often they can breed??? Ready for this?
Guppies are the rabbits of the fish world. They can actually have FOUR seperate matings growing at once. Takes about a month of gestation, but with four batches cooking at a time, they can have litterally 30 young a WEEK!
Mind you, this is possible, not average. Still, pretty astounding don't ya think? and ouch! Glad I'm not a fish.