Hi there! I would integrate the 4 & 8 week chicks together first and let them grow until they are approximately the same size as your yearlings. That would take them to almost point of lay. I suggest this for 2 reasons. First, chicks need higher protein levels in their feed than your hens...
To me that blue looks a lot like my blue Ameraucana. It also has slate coloured legs with is an Ameraucana trait. Orpingtons have white legs. With the Ameraucana's or EE's, a single row of peas is a pullet, while 3 rows is a cockerel. They take longer to be sure. If you can post a better...
The pullet's comb will also get red as they get closer to lay...in fact, that's one of the characteristics of a pullet ready to lay a first egg. However, as chicks - a pullet's comb should stay pale..yellowish?...not red/pink. The young roosters will have combs that go red a LOT faster. Then...
I'm leaning towards tenley being a roo - and nugget a pullet. Tenley's comb has 3 rows and is pinker. Nugget has one row, is narrower and isn't as pink..
My experience with the Marans breed is that the pullets feather out faster...so by 2 weeks, the ones without tail feathers and lots of down still - I would lean towards roos. Also, the boys in this breed rapidly develop their comb. Pronounced comb is going to mean roo. Best of luck with your...
Nice looking chick! Is it an Ancona or Exchequer leghorn? Those breeds develop more comb even as hens than others - so, if that is the breed, I might lean towards it being a hen. If it's a mottled orpington...then with that comb, I would say roo...