You've got Production Reds...at 7 weeks, and older, it is pretty safe to say you've got all pullets. Roosters at this point, as you've seen, will have substantial comb growth.
The remaining birds are acting as they are because you removed a bird and added another one completely upsetting the pecking order. It will take several days to several weeks for it to fully settle again...usually after a couple of days to week harmony ensues as all understand their proper pecking order in the flock.
This happens with all genders. It should never cause any bird undue distress or harm. Blood should never be drawn. No one should be starved.
It can help to place feeders at opposite ends of the coop/run/yard area so that there is more opportunity to get a good snack and drink, even somewhat on the run. Always have places a younger bird can hide from older birds. The seven week old will be hazed by the others as it is seen as an intruder at this point, and that may last until it gets more in size with the others.
If hazing gets too vigorous, it usually is best to give the new/younger birds slower introduction through fencing and allow them to free range together during the day but sleep separately. Then after about a week or two, open things up so that all have equal access. Usually by then, while there is a clear pecking order and the younger/newer is usually on the bottom, everyone is working together as a flock with nothing more than the "I get to eat first, then you do" bump and posture.
Edited by Lady of McCamley - 11/25/15 at 11:18am