Looks like a cockerel to me, but could change in the next few weeks. Is the bird from a hatchery/feed store or from show quality parentage? If you have other silkies, do this bird stand more straight and upright? Does it "act like a Cockerel"? I'm talking grabbing onto hens necks and not letting...
Take your feed out at night when they sleep. Did you fix her splay leg yet? Is it confirmed it's a she? Cornish Cross cockerels are sometimes better off getting butchered because they get much bigger than the females.
About your silkie cockerels, are they healthy? It doesn't seem normal that...
Some cockerels crow awfully early. It's not unseen that they start at 5 weeks. You can post a private YouTube video with anyone with the link being Able to see the video and put the link here. Some photos of the bird might be helpful.
I agree with @JedJackson but 3 still has hope.1 and 2 Is definitely a Cockerel but maybe wait another 4 ish weeks before you make any decisions about 3.
Brown one is a red sex link, also known as Golden comet, cinnamon queen, Isa Brown, Golden buff, and like 80 other names. She'll be a great layer. I will need a more clear photo of the white one only. Maybe a white rock or leghorn
1 is a pullet.
2 looks like a red sex link and if she's not, still looks like a pullet to me.
3: That looks like a rose comb and they are much harder to sex. I'd say Cockerel for now but it's worth waiting 3 ish weeks to know for sure.
4. Pullet