That's right. Under Certain conditions.
Don't give them a reason or an opportunity to fight and you shouldn't really have a problem. If you do it wrong they fight. If you do it right they live and breed happy.
Good luck
In the years I have kept partridge and pheasant I have NEVER had a problem with canabalisam or bad fighting. They feather pick every now and then but it normally never gets bad and if if does I swap the birds around a bit and it fixes the problem, my pens are 9'x5' and I keep about 6 partridges...
They are beautiful partridges mate. I don't think clipping there wings will make a difference. Because the pens are only 2 foot tall they will jump that high easy and smack there heads anyway but because they are only 2 foot tall it's not really high enough for the birds to get to much speed up...