The first thing you need to do is check your state laws concerning having pheasants. In my state, a permit from the G&F is required to have any type of pheasant. The permit has to be acquired before any pheasants are obtained. One step in getting a pheasant permit here is that the property and housing has to pass the G&F inspection. Part of that requires that where they are to be kept must be escape proof. That includes a run/flight pen that is covered by netting to prevent escape by flight and wire buried in the ground to prevent digging out.
This type of set up is not required for guineas but might not be a bad idea. When I had pheasants, I kept them separated from the chickens and turkeys (didn't have guineas at the time).
I suspect that if kept in the proper quantities with lots of personal space that the guineas would keep to themselves as would the pheasants. If kept in cramped quarters as so many people seem to try, I don't think it would go well with either species.
