They are mixes. Not ISA Browns, you're right. The ISA is itself a four way hybrid mix.
There are so many variations on the commercial Leghorn mixes and European poultry corporations like ISA, Tetra, etc, have lots of mixes based on light Sussex as well. All kinds of "names" are used to sell these. Of course, none of these are proper breeds, but these hybrids often make super good layers.
If they are older than 10 weeks, they'd be pullets. Most single combed birds have this in common, the males show themselves with large, red combs and red wattles at 6-8 weeks. These birds are starting to redden up, but this is the age, 11 weeks, that's when the pullets also do this, especially the top laying hybrids. Since they often begin to lay at 17 weeks, they mature quickly, but never as quickly as the cockerels.
The also have dainty legs. That's usually a good female sign as well. I see red ear lobes, I believe. In most birds, that means a brown egg.
They look like pullets. I agree some type of leghorn based hybrid layer--amberlink, tetra tint, there's so many coming out each year I really don't keep up with the characteristics of each.