I've never been good at telling the sex on BRs even when they get older than that but on it's face, it does look like the hens I have when they were pullets. And now they have huge red combs and lay some lovely eggs, there were many times before they started laying that I thought one or the other must be a rooster with the way their combs developed but then they both started giving me eggs and neither ever grew spurs.
As for the SLWs how old are they? I think mine are still younger than yours so I'm not sure about the combs but I'm interested to learn if someone has more insight. I've learned a lot about the Wyandottes but comb development wise I'm still in the dark.
I have no idea about the SLW, but the BR is for sure a girl. The females will have black on the front of their legs normally, and they also feather in looking pretty much black in the beginning. I have a pair of young BR, and the pullet is still a lot darker than the cockerel is. The male BR will feather in with very noticeable bars, the females just look polka-dotted at first..