What is the advantage of combining the rudder and brake pedals in aircraft?
All of the aircraft that I have ever seen have the rudder and braking functions combined into one set of two pedals.  To operate the rudder you press on the bottom part of the pedals, so that they slide back and forth on tracks, and to operate the brakes, you press the top part of the pedals so that they rotate towards the floor.  The left pedal operates the left wheel brake, and the right pedal operates the right brake, so you can use differential braking to turn the plane.  For rudder operation, the motion of the two pedals is locked together (i.e. press on the right pedal for right rudder, and the left pedal moves aft while the right pedal moves forward).  

Because of the two different motions (rotation for brakes versus sliding for rudder) there isn't a problem with hitting the brakes when you want rudder or vice versa.  Typical early training is to operate the rudder using your toes on the lower parts of the pedals, so and to only put your whole foot on the pedal to actuate the braking mechanism.