Thank you so much to everyone for all your help, great to get some input on things to take into consideration when trying to make a happy flock of birds.
With the 3 roosters we are planning for them to get their own hens in time, we are getting 10 chickens of each breed, first 10 arrive at easter. The ones turning out to bee roosters among them will be taken out.
So keeping two of them together is just until the sussex get to the 6 months, but maby it's safer to split the boxes now so we don't get any fights.
I guess we'll give the cochin some hens, the wyandotte by itself and the sussex roosters together until taking 2 of them out.
Also thank you for patience with my wobbly written english..