They will only fight if you have less than like 15 hens to each roo. (So if you have 30 hens, you could have 2 roos). If you only have 3 hens I wouldn't even get a roo, unless you are hardcore about getting babies, I think thats too much "action" to distribute among only 3 birds.
If, on the other hand, you did have 2134 hens, a couple of roos would be VERY happy!