Tracey - hopefully they will eventually live in harmony. When I had cats, the most I ever had at one time was 3, and they always got along great. I guess that's why when I read of folks here having to separate theirs so they don't hurt one another, it just seems so strange to me. I guess I was just fortunate. The 2 of my son's cats in residence here are fine together, female twins that were litter mates, so that may make a difference. It must be nerve wracking having to play referee all the time.
Good luck with them, and maybe time and patience will make a difference.