Thanks everyone for the help. I just put 1 new pig with the old one in a small cage and left them for a bit, then switched the new ones and let the second one see the old pig. I was so amazed as soon as I put the first one in there, they just looked like they had known each other all their lives. No arguments nothing, and the same happened with the second. Then when I put all three together they were sweet, no fighting they started grooming each other and themselves. They couldn't have cared less about each other.