Hi, welcome from Louisiana, glad you joined.
What do you mean by cull?  Kill them, eat them, or just remove them from your flock?  Cull can mean different things to different people and that might affect how some of us respond. 
As Mrs K said, you can keep them together until you can't. Some of that could depend a bit on how they are housed, the more room the better.  Some of that can depend on your expectations and tolerances.  What I might consider normal and typical behavior someone else may consider it an emergency and want to call out the national guard to restore order.   
We should be able to make a pretty good guess as to sex at ten weeks for a RIR.  If you could post a close-up of the head of each one you have a question about, we are looking at the size and color of the comb and wattles.  A second photo showing the legs, posture, and body shape could also be very helpful.
There are many different things you could do.  The main question is what do you want to do with them?