My broody hens will sit a clutch of five. I mark the eggs I intend to let hatch with an X and every morning when I feed I remove the excess eggs. Ten are too many to leave in a clutch, because the hens have to turn the egg several times a day to keep the embryo from sticking to the shell. The fewer the eggs, the less chance they have of being broken.

Are they fighting over who gets to sit on the eggs, or are the laying hens rousting the broodies? If you are letting eggs accumulate and THEN hoping a hen will go broody, you may be putting the cart before the horse. Don't let eggs sit unless you have a broody, and then if you want chicks, isolate her and her eggs to a private nest & pen. A clutch should be about 5-7 eggs.

Also, is the nesting material thick enough?

Velvet ~:>

Hmm, that's what I used to do, was to just let the eggs accumulate until the hens started brooding. I didn't think that they would start to set with just a few eggs in the nest. In past years I've had hens raise about 10 chicks --
I put lots of straw in the box, but they seem to move it around until it's down to the wood. I've put out wooden crates and leaning boards. Sometimes they seem to take to the site, sometimes they don't .
The best hatch I had was my first year, when one of the hens just disappeared on me, to come out later with about a dozen chicks. That's why I have been letting the eggs build up.
If they were going to get broody, they should have done it by now. I don't relish having to buy an incubator, but I need to get my numbers up. I have the Chanteclers, and we need more Chanties.

When my hens go broody, it's like Velvet says. They'll fight to sit on ONE egg. LOL. That's my signal to let them accumulate a clutch. Laying hens will also push a broody hen off a clutch to lay more eggs over it. Sometimes I'll catch two hens at once trying to shove the brooder off her eggs.

Hens will lose some feathers on their breast. This is a brood patch, and allows more warmth to press against the eggs to keep them the right temperature. If you have a lot of eggs, not only do some end up on the bottom and at risk, some end up at the periphery of the clutch and don't get even warmth. Broodiness, if it hasn't been bred out of a chicken is signalled by day length. Hardwired in.

Well, this batch of hens just isn't interested in having kids. It shouldn't've been bred out of them, as my original hens were quite good at this, and the ones I have are all descendants (with an occasional new rooster thrown in to keep the blood lines open).
I had heard that Chanteclers were not good brooders, but my first few years with them was just opposite.
1. Could the pens be too big. (they're about 24' long, one is 7' wide [3 hens, 1 roo], the other is 12'wide[13 hens, 1 roo]) I've tried to give them lots of places to hide.
2. I let my dog go with me into pen. Would that put them off brooding. She would hate me, but I could make her stay out.

When mine go broody, they seek a small compartment. I have the standard laying boxes mounted on the walls, each one holds one hen comfortably. A hen will see a clutch where other hens have laid, and then claim it for their own. Do your's just lay in the bedding?

YES, keep the dog out! Even if they are used to the dog, it's still a predator and may be keeping them from feeling safe enough to hatch chicks.

As for the nests, I use wooden nest boxes enclosed on all sides except the front, which is open. The bottom front has a lip about 3 inches high to help keep the nesting material in. I hang a curtain of heavy-duty black landscape cloth across the front of the box, slit up the center so the hens can come & go. It gives them the feeling of 'hiding' their eggs in a darkened nest box, which hens seem to prefer.

Do Chantis have any breed quirks where they PREFER to lay on bare wood, or anything like that?

I don't think the size of the pens themselves would make a difference, unless they were too small. Are you doing anything differently now from what you were doing when you first started and had success breeding them?

You might try placing some wooden eggs out as a clutch to try and encourage broodies, that way you wouldn't have to worry about breakage or spoiled eggs. I'd also make sure they have plenty of fresh greens and stuff like that to help trigger the natural 'Spring is here>there is plenty of food>time to have babies!' instinct.

Velvet ~:>