As I understand it, the 28X1 has only two separate PWM channels.
One of those has Enhanced PWM capabilities which allows four lines to conveniently drive a H-bridge directly, but all four lines are simultaneously controlled by the same PWM channel and are not individual PWM channels in their own right.
In "Single Mode" a PWM output can be routed to one or more of those four outputs and those selected will all output the same PWM signal. It would be possible to adjust and switch PWM rates while cycling through outputs, but PWM would not be continuous and simultaneous from all four lines.
That could be used to set four channels of analogue outputs using RC circuits, but unlikely to be usable for controlling four motor channels which needed continuous and different PWM signals to control their speed.
It is all quite complex, but the answer I think you are probably looking for is -- It is not possible to have four consecutive PWMOUT commands which would set PWM for four separate outputs independently which would all run without further program intervention.
