A radio button will usually have a Checked property that you can set. Alternatively, you can call the PerformClick method, but that will either check or uncheck the control depending on its starting state.
I may not understand your second question. To click on controls in a pop-up, you'd interrogate them like you would controls on the main window and call the appropriate method to click them.
I am not sure what you mean. When you are performing interrogation, you may right-click on a matched control and select Test Methods to trigger the same methods you'd call in an automation. This will allow you to see what works and what doesn't.