No they do not! For example Front Rotors; if one rotor surface when turned on a lathe will exceed limits of safety (i.e. cutting away more metal from the rotor than is safe as regulated By D.O.T. (Department of Transportation ) then you need to replace the rotor. If the other turns out to only need a small amount of surface removed to make it usable then that can be done. Same thing applies to the rear disc brake rotors. Of course if both rotors are beyond safe resurfacing, then both should be replaced. HOWEVER it is possible that having calipers of a different thickness may cause them to perform differently causing a potential safety issue due to the fact that they will not have the same heat dissipation characteristics. I have not experienced this myself but this does seem to be the basis behind the recommendation of replacing them in pairs. IF I were to worry about then, I would probably only be concerned on wheels involved in steering.
Yes you do
The brake rotors only need to be changed if they are worn beyond allowable specifications and should be changed in pairs. They do not need to be changed with the pads unless they are damaged as above or warped.
You can purchase one or more.
No just the bad one.
Possible that the rear sensors are broken.
You can buy just one.
It could be that the brake pads are dragging on the rotors.
When rotors need to be changed usually the pads have worn down. It is always a good idea to change pads when changing rotors.
Aggressive driving.
Brake calipers are the hydraulic devices that wrap around the rotors and pinch the brake pads into the rotors when you stop.
You can get your brake rotors replaced by visiting Autoparts Warehouse which contain various brake rotors in size and durability to fit your needs and accommodate your budget.
mine did the same thing and would not stop until i changed the brake lines also, then it stoped.