I added 6 hens last Oct and am thinking this one is a rooster. Looks different than the rest - stands taller, large tail feathers. Also, I rescued another rooster, not a sexlink, and his posture is similar. How do I tell?
That one is a rooster, but not a sex link - a black sex link rooster would be black and barred and a red sex link rooster would be white with red in the shoulders. Yours is probably a production red.
There shouldn't be any trouble - multiple roosters can get along. Just make sure they aren't causing damage to the hens by overmating them like feather loss and injuries - if that happens you'll need to get more hens or rehome one of them.