1 Rhode Island red
2 Blue Andalusian, blue Australorp, blue Orpington, blue copper Marans
3 Partridge Plymouth rock
4 Welsumer
5 barred rock
6, 7 maybe Easter eggers
8 same as #2
9 cuckoo Marans or maybe olive egger
I edited, but it still might be off
12 weeks is when the males usually start showing male specific feathers. Those are the long, slim, pointed feathers males get in the hackle and especially the saddle area.
But in the meantime just keep an eye on the comb and wattles for increased size and redness. If things stay pretty much the...
As far as space goes, I think you'll be okay for another couple of weeks. But then you should move them to a bigger space.
As far as the heating plate goes, I would probably leave it the way it is for a while longer, until some of the smaller chicks get more feathering.
The comb/wattles are pretty well developed for that age, but not to the point where I'd say it's for sure a male. I think this one will simply take more time than most to tell.
You have no Wyandottes or Brahmas, so they must have substituted other breeds.
1 is probably an Easter egger
2 is the Leghorn
3 I'm thinking it's another Easter egger, but could be a brown Leghorn or Welsumer. That color pattern is pretty common.
4 olive egger
5 Hmmm, the feet look yellow...
She's a pretty hen. Whether she's a JG or not, I wouldn't use her for breeding purposes because, as you already stated, she's way under weight, and she also doesn't fit the standard for Jerseys in other ways, such as the long, high carried tail. I'm sure she'll make a great pet and laying hen.
It's difficult to tell olive eggers and Easter eggers apart. They're both hybrids, the only difference being the OEs should have the dark egg gene plus the blue egg gene, whereas Easter eggers can lay any color, really, but often blue or green.
In the picture, the blue one in from is a cockerel...
If it is 8 weeks old, then probably a male with comb and wattles of that size. It does look like a cuckoo Marans cross, maybe with one of those Legbar type Easter eggers with the little crests.
There are two types of cinommon queens. Both are sex links. This type is a red rooster over a silver laced Wyandotte hen, so they look different from other types of red sex links.
This is a question that would probably get answered more quickly on this forum: https://www.backyardchickens.com/forums/exhibition-genetics-breeding-to-the-sop.16188/
Maybe @NatJ can help.
Laced Wyandottes often get large, colorful combs early, even in the females. So in the case of this breed I wouldn't go by that alone. I would wait another few weeks before deciding. The thing to watch is the evenness of the lacing on the back and shoulders. Females will be more even in that way...