If a freight train has two locomotives, do they both pull equally strongly on the freight train?

Answer

The force exerted by a locomotive on the train depends on many factors, such as the coefficient of friction between wheels and rails, but the main factor is the electric current through the motors. If the engines of one locomotive are not supplied with power, that locomotive will not exert any force and will simply be pulled along (provided, of course, that the other locomotive is powerful enough). When several locomotives are used in modern trains, a regulation (with communication between the locomotives) is provided that ensures that both locomotives pull approximately the same speed by regulating the current through the motors.
The same happens in trainsets that run without a locomotive: there is a motor on each set of wheels and the control ensures that all wheels pull approximately equally hard.