Everyone is thinking you use a stone or smokeball to evolve eevee into these two rare evolutions. They are wrong.
Wrong ways: Stones, smokeball(umbreon)storing in PC box, making it faint a lot, or never using it in battle.
The right way is to keep your eevee with you, make it battle without fainting, giving it vitamins, or leveling it up with the right amount of friendship points. In the morning or day, it will become an espeon. At night, an umbreon. I hope this helps you get a rare Pokemon.