They used both light and dark Force powers for the good of the Universe.
NO THEY DIDN'T. There is no Grey anything. No Grey Jedi, No Grey Sith, No Greyside, No Neutral side. There is only a Darkside and a Lightside and you are on one or the other because that's what canon has always said.
The EU, the Video games, none of them have ever been a part of canon for one single second. 7000 times it's been said by the copyright holders, there is no Grey.
We don't get a say in canon, canon is whatever the hell they say it is. That's what copyrights are for.
The entire 'grey' movement horseshit is purely a fandom creation. The only one exception and only one time was when Qui-Gon Jinn was referred to as a 'Grey Jedi' but that term meant lightside jedi who sometimes broke the rules. Qui-Gon never used the dark side one single time. That is literally the only time 'Grey Jedi' is ever used in canon. Every other time it's pure fanmade mary sue, special snow flake horseshit.
You're either a Star Wars fan or your not. If you think Grey should be a thing, you're not a Star Wars fan. When people are fans of something, they don't want to see them changed.
Details not known.
The Order sought out similar orders to form alliances with. They made contact with the Night Jedi, who sent Jobie Wan Kenobi to act as ambassador. They agreed to an alliance, with students from either order taking part in exchanges with the other order, and military support if it was asked for. However, the alliance was not often used, and communications between the orders dropped off. The Grey Sith didn't form an alliance with the Light Sith because the Light Sith were wiped out.
The GSO were attacked on Ossus, and after a battle, were forced to retreat. They contacted their allies the Night Jedi, who offered them sanctuary on Endor, but they were not heard from again.