So they are roughly 2 months and 3 months old. Sometimes chickens of about any age can get along fine but often the more mature will pick on the less mature. It’s part of establishing the pecking order. If a lower ranking chicken enters the personal space of the higher ranking, the higher ranking is within its rights to peck the weaker chicken. Usually the weaker just runs away and quickly learns to avoid the stronger to start with. There might be some chasing involved but usually as long as the weaker runs away things are fine. A huge problem comes about if the weaker does not have room to run away or gets trapped in a corner or some place like that. The stronger takes that as a challenge to its social position and will keep on attacking.
How long does this last? Until the weaker matures enough to force its way into the pecking order. With pullets this is usually around the time they start to lay, though that can vary a fair amount. Each chicken is an individual with its own personality.
You can read my thoughts on space if you follow the link in my signature below. In Wisconsin in the winter I think you will need more space for them if that 8x5 is all you have. That could be a separate coop connected so they can go back and forth, make that 8x5 quite a bit bigger, or build a run and try to keep the worst of the snow out of it. One way chickens have learned to live together in a flock is if there is a conflict the weaker runs away from the stronger or just avoids them to start with. That’s what I was talking about above. With an all-hen flock it’s not usually too bad once they all reach maturity but if you crowd them you can still have some pretty drastic behavioral problems.
There are general rules of thumb for nest boxes. A minimum size is 12” x 12” x 12” for full sized hens though they will crowd into smaller nests. Also the general rule is one nest for every 4 to 5 hens. Size has something to do with that. It’s not that unusual for 2 or even 3 hens to crowd into one nest, even if there are empty ones available. The bigger you make a nest the more hens it will service. Also if you ever let a hen go broody and hatch eggs with the flock, the chicks that hatch first will climb up on Mama’s back. If the nest is so small that Mama is near the edge the chick may totally fall out of the nest when it falls off Mama. That’s not good. Also if one of your hens goes broody she may use up one of the nests until you can break her from being broody. Most broodies are willing to share a nest but some won’t. I’d suggest for nine hens if you build the nests maybe 16” x 16” you would be OK with two nests, but if you go closer to 12” x 12” you might want three.
On average my brooder raised chicks start roosting at night is 10 to 12 weeks old. I have had some start a lot earlier and some a lot later, but 10 to 12 weeks is fairly normal. Until they start roosting they generally sleep in a group in what they think is a protected corner. I don’t think your choice of bedding has as much to do with where they are sleeping as their sense of security. Do you have roosts higher than the nests will be? Their instinct to roost should kick in pretty soon and they will look for the highest place they can find to spend the night.
Thank you in advance. 
