A good multi meter can tell you how many amps each of the motors draw.

Just hook up the motor to a battery, put the multimeter between the motor and the positive connection. Let the motor run, and read the amp draw. This will give you the unloaded amp draw. Then pinch, or otherwise slow or stall the motor shaft as best as you can. As you do this read the meter and it will tell you the loaded or stalled amp draw. Stalled will be the maximum amps the motor will demand.

That will help determine what kind of rating the ESC needs.

Being handed down over so many years, is it an Electronic Speed Control (ESC) or
is it a wire wound resistor with a mechanical wiper contact? Any pictures?