I outlined the male specific feathers in red here. On males the sadle feathers at the base of the tail are going to be narrow and pointed, on females the feathers at the base of the tail will be broad and rounded at the end.
On the lighter colored male I also outlined the one obvious sickle feather in the tail in red. Sickle feathers are the curved tail feathers found in roosters. They're usually also pointed, but since their much broader than saddle feathers the point isn't quite as sharp. Females will have straight tail feathers with no or very minimal curve to them. Tail feathers are not the best indicator in young birds though because it takes longer for them to come in on males and most females go through a wonky stage where the tail feathers can appear curved even though they aren't.
The areas circled in teal are the rusty/red shoulder patches I mentioned in my previous post. Females can have red in these areas, but it's usually a lighter shade of red and a more uniform color. Especially in mixed breeds and easter eggers that color in those areas usually indicates male specific coloring.
In the darker bird, the black breast feathers is a male specific color pattern. Females usually have the lighter colored feathers on the head and neck and lighter colored/brown breast feathers.
Comb and wattle color is another thing to look for, but not particularly helpful in this case where you don't know a rough age of the birds. Pullets will start to get red combs a few weeks before they start to lay, cockerels will start to redden much earlier (sometimes as young as 2-4 weeks old).
All chickens have spurs, male or female, the only difference is size. Males develop much larger spurs than females, but this trait takes the longest to develop of all the secondary sex characteristics.
This is a spur on one of my 8 month old cockerels. As you can see, it's not very big but it will get bigger with time.
This is a
3 year old rooster from another thread on BYC. You can see his spurs are much bigger. You can also clearly see the curved, pointed sickle feathers in his tail.
This is one of your cockerel's spurs. It's about the same size as a female of the same age would be, but it will get bigger.