Chicks cannot be born with coccidiosis. The coccidia oocysts (eggs) that are in every single chicken poo must first be sporulated and have excess amounts ingested causing a bloom... Taking not less than 4 days before symptoms start to show... most likely to happen in warm humid places similar to that of a brooder. Easiest spread by dropping getting in the water... but I have seen chicks take a drink directly from their hatch mates waste.
https://www.merckvetmanual.com/poultry/coccidiosis/overview-of-coccidiosis-in-poultry
It will effect the weaker birds first. All have individual immune systems.
Yes, Its my fault; I built a "super brooder", for my "fancy chickens" and it's very nice (for chicks I suppose), just one mistake I made when I installed the water nipples into the PVC caused a small, occasional drip into the cabinet. You know the rest....warm, moist, hatching, eating. I first thought it was the shavings, then after removing them, moving the birds inside, and a small amount of research-my mistake was evident. I think the girls got it first, then the roo pictured in OP, so I just treated the 6 silkies, even though I only had 3 exhibiting symptoms.
We send them to freezer camp here.

Life is too short for mean birds, Silkies included. Surprisingly the Silkie cockerels are often bigger jerks than my large fowl boys. It's like they got little man syndrome or something.
Look forward to the new pics.
I should have took them today. They were so rambunctious.
Pip is the bully! Jeez a pete, I wish he'd give it a rest. I've never eaten a silkie before, but we've been discussing his fate.
My daughter and I found the lighter ones to stink a bit more than the darker Silkies. Maybe they have more poo stuck to foot feathers that other birds do not... and then scratching themselves, spreading the smell onto their bodies... Broody makes it worse!
I don't treat all chickens unless there is a reason to... like pasture conditions being too crowded or endless rain in a warm location type thing. But it won't hurt them if you choose to treat. I just try not to over use thing so that resistance doesn't become an issue when I really need it to work. But you should do what you think is best with the information you have. If you learn something new in the future, switch it up.