The way to control Eevee's evolution is about the timing

I evolved 4 eevees in a row and like a round robin, it gave me a Jolteon, vaporeon and flareon, but the 4th one was vaporeon. So it gives equal random chance for the first 3 and probably again random after that..

No way to control its evolution, but a onceworking nickname trick, I evolved 6 evees and got 3 vaaporeons and 3 flareons, but no one jolteon, but don't need it too much

Nope, you're wrong. Plenty of youtubers have evolved separate Eevees at the same time and got different results. It's random. Don't waste your Eevee candies guys.

I was trying the mentioned technique of how it might rotate to try to get a second vapor. It didn't work as they said but I had a bunch of eevee candy so I just evolved a bunch. It was awhile ago but I think it went like flareon flareon then I got a vapor then I evolved a few more and ended up getting 3 vapors in a row all with wg/hp moves. I felt if I kept evolving they'd just keep coming but stopped as it'd be difficult to power them all up. They are my main gym attackers

I evolve Eevees quite often as I can catch them almost everyday. When I get only Jolteons and Flareons for the first 2-3 eevees, I will stop and wait for another day.
I hear some trainers sharing tips that a Swift eevee will more likely become Vapos, Dig eevee will become Flareons and Body Slam eevee will become Jolteons but I haven't tested that.