Game Hens make very good mothers. They are extremely agressive towards anything that comes near. Even humans. But they will most definately kill your chicks if you try to put them together. Whether they are broody or not. They will kill another hens chicks even if they are broody at the same time. They are extremely protective of thier own brood. I know this from experience. I don't know how they know their own chicks from others but they do. I have tried three times over the years to introduce "other" chicks to three different hens that were already brooding a clutch and every time they were killed within 2 hours. I thought each time it may have just been a bad hen. I do not know why this is and there may be other breeds or people that have had it to work but I believe it is a strong instinct in them that causes this. I will never try it again with any hen. I thought as your dad does that because they are such good mothers that it would work but it don't.