At 8 months old, if male, male specific feathering should be fairly obvious.
You would have to post a very crisp, clear photo of the bird for gender ID.
The rooster ejects his sperm into the vent of the hen. The hen then shakes it into a holding sac for fertilizing the yolks. There is no penetration of any kind. For a hen, the portion of the reproductive tract that joins the cloaca is call the oviduct. In a rooster, it's call the vas deferens...
Pictures of random body parts really doesn't help. A full body shot, that shows the details of the feathers really well is what is needed. Also, knowing how old a bird is, is key.
The Marans are all definitely cockerels. The Ameraucana are probably pullets. Need to be able to enlarge the pictures to even try to guess the Wyandottes.
It's really hard to get a good photo of saddle feathers on a white bird. I suggest you take a close look at the feathers on the backs of both birds. Pullets have broad, rounded feathers. Males, by 4 months old, should have some pointed, narrow back feathers.
The darkest one is a cockerel. Do you see those really shiny, pointy feathers coming in on the back? Those are the male saddle feathers. The bird towards the middle also has very obvious male saddle feathers. Take a close look at the back feathers of the rest of them.
Can't really help you until you post some better quality photos. They need to be very crisp and clear. The ones you posted are too blurry. When taking pictures of chickens, you must be very patient and still.