When another gelding was introduced to Gem and Vega, we just turned them out. I'll call the horse we turned out with Gem and Vega, Bob.
Bob was very vocal and threw some strikes and tried to bite and kick, but Gem and Vega walked up to him, and then walked away.
Gem does get protective of Vega, but the "fighting" only lasts a few seconds and then everyone goes their separate ways.
Since putting Bob in with Gem and Vega, we have added another mare, i'll call her Flower, and when she's in there, everyone's very happy. Flower and Bob stay together and Gem and Vega stay together. It's only when Flower or Vega comes out that there's problems. But none of the horses have been injured or anything.