Since there are essentially 3 levels of seating in coach now it seems to me that it should be
- if all members of your party are seated in PE then it is ok for a GA or FA to ask if swapping of seats could occur in that section.
- if all members of your party are seated in main cabin (not saver and not PE) then it is ok for a GA or FA to ask if swapping of seats could occur in that section
- if all members of your party are seated in Saver fare seats then it is ok for a GA or FA to ask if swapping of seats could occur in that section
(asking does not mean you must swap)
What is not ok is to ask someone from PE to move back to main or saver seats without at the very least tried to maintain the seating of the other passengers choices (which can often be a cost difference). I am not sure why it is ok for a passenger to pay for a PE seat and then be required to move to the back in favor of someone that did not pay for that section. It does cost more to fly with others, there is no way around that.