Presume these are ordinary pheasants, not ornamental?
Game birds need much more protein than chickens, so ensure you feed dedicated game bird (or turkey) crumb/pellet.
Also be aware of a game bird's natural behaviour. When alarmed their instinct is to scatter -chickens do the opposite - they flock. So if you intend to let mum and babies free range and something scares them the chicks will scatter to all four corners of the earth, resulting in a very stressed mother hen and most likely you as you wait for them to find their way back to mum. They will, eventually, but it may take some time and they will be at risk of predation.
For all her good intentions a broody hen won't be able to instil the same sense of preservation that a mother pheasant would. Bear this in mind if your plan is to "release" them into the woods at some point. They may also find their way back home, attracted by sounds of the chickens they have grown up with, and may possibly bring some friends with them. I find pheasants seem to attract other pheasants and you may wake up one morning with rather more in the garden than you bargained for, especially if you are feeding chickens nearby.