I only see 3 Barred Rocks in that photo. The cockerel on the far right is quite obvious. Enjoy your chicks.
At 5 or 6 weeks, both kinds will be easy to sex. On the red sex links, the males will feather in mostly creamy white with a stray rusty feather on their upper wings and back. The comb and wattles will sprout noticeably red, while the pullets will be mostly rusty feathering and their combs will be dull yellow and no wattles at all.
On the BR, the same. The males will sprout red combs and wattles at 6 weeks, while the pullets will show no secondary sex characteristics involving combs and wattles at all. Dull yellow.
On the BR, the males will be silvery appearing as their double barring gene makes their white really pop, while the pullets, with only one gene, will look dark, blacker in contrast.
Easy, very easy to sex at 5 or 6 weeks. You'll know for sure.