I'd try it. If you were a month later in Massachusetts I'd say no. They grow really fast. You never know how many you will actually get but she should be able to cover all of them for as long as she needs to since they should hatch within a week from now. Brahmas are large hens and you have different breeds so they will be different sizes. I think you will be fine. In the heat of summer I often see baby chicks sleeping next to Mama, not always under her, even when they are pretty small and lots of room.
When I was a kid on the farm we had one hen that hid a nest and brought off 18 chicks. I never found that nest so I have no idea how many eggs she actually started with. She raised all of them. A couple of times I've given a broody hen 15 chicks, some she hatched and some from an incubator but all the same age. They did fine.
One suggestion though. I don't know what color of chicks you are hatching. One time I had a broody hen hatch a couple of red chicks and gave her a mix of red and black chicks from the incubator. Her red chicks were a tad early so she bonded to them. When I added the other chicks she accepted the red ones and rejected the black ones. I had to raise those myself. The funny thing was that she had raised a mixed color brood earlier that year. How common is this behavior? I don't know, I'd successfully done this before with other broody hens. You might consider giving her eggs that she is likely to hatch different colored chicks. It probably isn't necessary but I would in your situation.
