Here are a couple of tips, but no quarentees. Do as you plan, put the new horse into a separate area where all horses can see each other. Then this is what I do after a bout a week, take the horses all out of the pasture you are planning on using. Put the new horse in there, on lead line walk them around the fence line so they can see the new area.Turn them loose. This horse will run and explore. While you are waiting for this one to settle, go and get the less dominate horse, the lowest in the pecking order, take them to the pasture, let them smell noses, then turn lose, after these two stop running and settle down to nibble on grass or hay, usually about an hour at most, start working your way up from the lowest to the most dominate horse, usally works most of the time, as the new horse will bond a little with the lowest member then find their way into the order of the herd. Good luck.