What you are saying I am pretty sure and just tested it but you can only select one radio button at a time no matter what. That is why it is called a radio button. If you want to disable clicking any other radio button after a user clicks one then you need to disable all the radio buttons when somebody clicks it.
Code:
Double click each radio button and put this code in
radiobutton1.Enabled = False
radiobutton2.Enabled = False
radiobutton3.Enabled = False