Do they get along? As long as they don't bite and kick, I'm sure it would be fine. They WILL have a pecking order, and let them figure things out by themselves. They will be as if in their natural place.
I have the same problem...we have 2 geldings and they've been together since July, then 2 months or so we added a TB gelding, he's a good boy and we have him seperated from the other two.But once by our choice and once by mistake w/in the first days they got in together and our 2 chased him thru the fence(hot tape).So I have decided to wait til June to put them all together when I can be around the entire time to watch everyone. I am just fearful because of our fencing that someone will escape and get hurt.But they are very much familiar w/ each other being next to each other and have played over the fence.Im hoping they get along, they all ride together good.
Good luck, it will work out, just be around to supervise their antics.