Nice little bunch of variety there. I believe, if these are only 4 weeks old, the Barred Rock is definitely a cock, the Golden sex is probably a cock, and even the Ugly one could be a cock. However I would put money on the others all being pullets.
Only time will tell, but I wouldn't mind knowing the outcome in a few weeks when all will be more certain.
Barred rock, the one you think is a RIR is a golden comet, The BR is def a roo, and the bantum might be as well... The one you think is the sex link is actually the RIR....
I think they are older then 4 weeks, more like 5-6 weeks and the bantam 8 weeks. Just by my experience with feathering.
The barred rock could possibly be a cuckoo maran. Look at the legs. Barred rocks have yellow legs and marans have pink/white legs. Females usually have a black wash on the front, but not always. I do believe that one is a boy. The comb should be much smaller at this point.
Here's my female at 8 weeks
4 weeks old
The rest look like girls. Also, your RIR looks more like a red sex link.