Those look like Leghorns rather than meat birds which is good news for the longevity of your birds.
Since they are leghorns and are 4 months, I wouldn't say for sure that they are all roosters. Some look rather pullet like to me. With leghorns many people confuse pullets for roosters because their combs are so big.
A Leghorn rooster would look more like this.
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Hens look like this.
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8-10 hens per rooster is a recommendation for the safety and well being of the hens rather than for the happiness of the rooster.