Welcome back to the forum and the chickens! We'll be looking forward to seeing you around more. Best of luck on getting more of those specialty breeds!
Cochins can be eaten as they're a dual purpose breed, but they can live long, healthy lives with no troubles. There's nothing to worry about with him. He'll be a nice addition to your flock if you wanted to keep him. (Some people keep Cochins as pets.)
I would remove all the chicks. The mother might eventually go after them, even if she appears fine now. I don't think the color (especially how it's so similar to the others) should be a problem. However, I have known brooders to be rougher with their sons than their daughters.
When chickens start laying, it's normal to get abnormal eggs. With Marans, their eggs are covered in speckles, which gives them that chocolate appearance, instead of a pigment. That being said, getting darker and lighter eggs is normal. I have heard with other dark egg layers from other people...
The little guy appears to be a Buff Sebright. The black one looks like a Minorca. The barred things look like Barred Rocks, though the lighter one is a bit too light (could be bad genetics, though still a good bird). The white one is a Cochin. Where did you get them and how old are they?
The first one is a Light Brahma and possibly a cockerel based off the redness of his comb. The other, I'm not sure. Could you post a picture showing more of its side? Where did you get them and how old are they?
They look like Silver Duckwing Old English Game bantams. Could you post more pictures of them, like a side view? I might be able to tell you their genders as well.