It really is not only about the number of males to females, a huge component of the success of the flock is how much space, and how that space is configured. More birds often times makes problems worse depending on the space, because more birds means less space for each bird. The question about if you have a duck enclosure and chicken enclosure is important. Space is very key and how you have that space set up. Is it an open rectangle? Is there hideouts?
So measure your set up, both coop and run. To get multiple roosters to live calmly together you need space, and luck.
Some roosters become very difficult to have. Roosters really do not have an understanding of sharing hens or this is your space, and this is mine. One will want it all, if he gets it, it is because he fought for it and won it.
Sometimes a pair of roosters will fight once and done, sometimes over and over again, causing huge tension in the flock, and sometimes to death, not pretty. Not good flock management. Sometimes too many roosters, constantly competing with each other, will keep claiming a pullet over and over again, wearing out your hens, also not pretty.
"Roosters are where the romance of having poultry meets the reality." (AArt)
IMO I would want about 20 + birds and the space for that many birds to keep two roosters. I have kept two roosters once in less space with less birds, but really it was not worth it. It decreased the enjoyment of my flock.
Mrs K