How will my two horses react if I add another?

I had just two fillies for a while that were a pair bond, we decided to get another horse we could ride as well, we ended up getting a gelding. We were not able to put them in adjacent pastures at the time so we just let them meet through the fence (we had the gelding on a lead rope on the outside) The horses do get pretty riled up and squeal and stuff but this is normal. We just gave them an hour or so to settle down (we let the gelding mow our lawn ;) Then we put him in with the girls. My horses are very friendly with other horses so I was not too worried about any one getting hurt. They make the whole thing pretty dramatic but they settle down eventually. Usually things get back to normal in a few days to a week, sometimes it could take longer depending on the horses. Though my horses are friendly they had disagreements on who was gonna be alpha lol. Six months later they still have their disagreements lol but as long as no one is getting hurt just let them figure it all out. Good luck on your new horse!