I have lost a lot of full size birds to flying predators. So if you are not loosing adult birds, I would not worry about it. However, a lot depends on the age of the chicks. If less than 3-4 weeks, the broody hen will have enough hormones to be very aggressive to anything else. But if over 3-4 weeks, she will be shortly forgetting that they were her chicks.
I get mine in the flock, as the flock is the safest place for them. If they are part of the flock, they will follow the flock's cues. I am assuming you have a rooster. A rooster dramatically decreases my day time predation. In keeping them separated, you are not letting the chicks grow up in the chicken society. Missing, (imho) a valuable protection.
However, do what you are most comfortable with. I do not think having two broody hens with different age chicks will work.
Mrs K