How do i introduce my 6 year old shetland to other horses safely?

I need a few bits of help, Ive just got a 6year old shetland pony, I have and understanding he is a stallion, (if this is correct) He seemed to have settled in really well and he seems to be rather happy he wears his head collar and walks on a lead rope but yet he doesn't seem to listen to me nor anyone Else for that matter i would love him to come to see me when i call him my ants horses did, lol :S but also where we have homed him two other horses have moved in and are now in the field next to him but there is Alot off aggression on both sides with Romeo kicking and rearing? and also the other horses biting and kicking, im very worried because i dont want any of them to get caught in the fence is there anything i can do, and is there anything i can to to help keep Romeo Happy?