To answer the last question as well as some natural follow up questions, here is some basic info on guppies in general which should all apply to the endler variety as well.
The eggs hatch inside the mother and the fry are then born free swimming (as already stated). Gestation is around a month usually, but females are capable of reabsorbing developing eggs, storing sperm for over six months, and slowing egg development. A single mating can produce dozens of fry every month for six to eight months.
Males always want to Kate. If they can't eat it, they'll try to... well, to be pg here, I'll say seduce.
Births can consist of as few as two (personal experience) to as many as a couple hundred. That many at a time is extremely stressful to the female and may result in her death.
All livebearers will eat their young if hungry enough, but endlers seem less prone to do so, especially if well fed. It's generally not a concern.
They reach sexual maturity somewhere around 3-5 weeks. True wild strain endlers are in demand and some people (raises hand) will gladly pay for them if you end up with a lot. Hint hint.