Go to page 164 - PWM mode. Check point number 5. Go to page 167 of the datasheet - the OCxCON1 register. Check bits 10-12. You can see that you can select any of the timers.
You can run all the PWM modules off one timer if you want. eg. if you want, all PWM modules can use only Timer 2 as time base.
Or you can rearrange however you want. Eg. You can have 2 running off Timer 1, 3 running off Timer 2, 1 off Timer 3 and 3 off Timer 4 without even using Timer 5.
Yes, you can control the duty cycle of each PWM module independently. Load the duty cycle and period values into the corresponding OCxR and OCxRS registers, as required. Use OC2R and OC2RS for PWM module 2. Use OC6R and OC6RS for PWM module 6.