Striped snails might be a few different species, not breeds. A pic would help enormously. Baby snails are well able to manage on their own from the moment of birth, but the ones you are seeing are not likely babies of the adult. They are more likely 'pest' species, bladder or ramshorn or pond snails. They will breed rapidly, at a very young age, don't need mates to do it either. Lay eggs in clear gel like blobs on any surface.
If you want a few small snails, these guys are not bad to have but they do reproduce constantly, so you have to pick some out or remove any egg masses you see. If you want hard working snails that won't reproduce, get a Nerite snail. Lays eggs, but they cannot hatch in fresh water.
Mystery snails get quite large, but lay eggs out of the water, so easy to control. Also have sexes, need both for fertile eggs, but females can lay infertile ones sometimes. Get to the size of a golf ball, in your size tank a pair would be plenty. Nerites are smaller, you could have 3 or 4 of them.
Nerites are commonly called Zebra snail, or Thorny or Horned, or Tire Track, etc. These are different species, but all do the same work, and all need salt water to hatch their eggs. Very useful snails to have, shells are quite handsome.
Mysteries come in an assortment of colours.. bodies can be ivory, gold, blue, purple, black, brown, etc., shells can be any of these plus they may or may not have stripes. Stripes are the wild form of the original snail and are often brownish or dull goldish under the stripes. They have long antennae and a breathing siphon they can stick up a couple of inches to breathe. Must have air, they are air breathers and can drown if they can't get to air periodically.
Nerites are totally aquatic, no air required, but can stand long periods out of the water without suffering. They come from tidal areas where they are exposed to air between tides a number of times per day.
