RawBenz

I've noticed the front brakes have been squeeking.
Are the brakes one piece?

Can i get away with just changing the brake pads or do i need to change the front discs too?

ML63 AMG

Rotors are super heavy 1-piece rotors. If the edge of your rotors have a lip and the cross drilled holes pattern has disappeared then yes your rotors are done.

I recommend the Racingbrake 2-piece rotors if you have to replace your stock units, they make a huge difference!