Most hens will fight over all the babies if there are two broodies. Our Key west hens will share chicks but none if the other breeds seem to. To be safe you should make 2 separate pens for each mom and babies in a shady area. They can be 4 ft by 4ft if needed to stay small. You can also use a large dog carrier in a pinch placed inside a pen area. You must have a small gauge wire to prevent the chicks from getting through. I have even had tiny chicks get through regular chicken wire. You can place either solid wood or small holed hardware cloth around the bottom to keep the tiny babies from getting through. There is also a black plastic garden netting fencing that is cheap and comes on a roll at home depo etc. you could zip tie onto the larger fencing.

Sams club has cardboard boxes that look like nest boxes that are cases for chicken nuggets etc. come in. They let customers take the empty boxes. These are perfect for broodies to set their babies in inside thier coops.

Here is a pic of the cardboard boxes I use from Sams club. She takes her babies in them at night. We built this little broody pen up off the ground. It is 6ft long by 4ft deep by 4ft high. up on 1.5 ft legs. It has hardware cloth and some plywood on back and sides. Mostly open wire for good air circulation. It has a solid plywood roof with roll roofing over it. We have fox, bobcat, possum, etc so it has to be predator proof here. This is one of the Key West hens with her 7 chicks.