I tend to think people who swear you cannot have two Roos in a flock "because one will kill the other" must have originally heard that from GAME chicken breeders, and it's just been erroneously attributed to all chickens in general and then perpetuated.
I have kept a flock with multiple cockerels and roosters (the numbers have varied over the past four years) and only had ONE rooster that tried to kill a smaller one. He was mean to hens and pullets, too, so he was permanently culled. There are ALWAYS at least two mature roosters in my flock; the dominant and his subordinate. Cockerels growing up within this flock have integrated just fine; the senior Roos let 'em know they are subordinate to them and the kids respect it.
In your flock, your roosters will probably settle into #1 and #2 positions, but your hens might be over-mated and suffer feather loss on their heads and backs. Less than five hens "apiece" ( it doesn't really work that way, evenly, but you know what I mean) means all the girls will get a lot of rooster attention.
Hen "aprons" or "saddles" may be necessary if that happens.
The two rooster dynamic is usually a good one, though, for most flocks.