Hoping there are some HVAC experts on here. I am mulling over the idea of adding either jumper ducts from each of the bedrooms to a central location where the existing return air will create airflow. Alternatively, I was thinking about putting 12 x 12 filtered returns in each room and connecting to the Plenum, where it will actually pull directly through dedicated lines. What are the pros/cons to using each of those methods?

The biggest challenge I have with the jumper ducts is inconspicuous ceiling space upstairs outside the bedrooms and not really wanting to have 4 registers that I will see in our landing area at the top of the stairs.

The only downside I see with gong to the return air plenum is whether it would create any imbalance of airflow that was previously engineered with the two large 16" x 25" existing air return points already feeding the system.

The goal is for the doors to be able to be closed while doing homework or sleeping and allowing the return air to escape from the rooms.

There should be a ~1/2" gap at the bottom of every bedroom door. Cold air goes into the room through the vent and out of the room through the gap under the door and back to the air intake to the AC. If you add an air-intake into each bedroom, Cold air will go from the vent to the return since that's the path of least resistance. You will no longer have cooled air in your hallways / landings /foyers etc and even less air flow to any closets off of the hall.

Are you saying that I should use jumpers ducts to remove the air from the room so it stays circulating in the conditioned space rather than just going right back to the AC in the attic?

I think he's saying that if your doors provide for the proper clearance at the bottom, you shouldn't need to do either. If they don't, it would be easier to trim the doors than to run any new ductwork.

A door with 1/2" clearance is going to be a choke point for return air unless it's serving a closet. The opening of a 6" round supply duct is 28sqin. A 1/2" undercut on a 36" bedroom door is 18sqin. Jumper ducts or return air ducts are not going to undermine cooling. Undersized return air path limits cooling effectiveness.

The goal is for the doors to be able to be closed while doing homework or sleeping and allowing the return air to escape from the rooms.

This is also the goal of many commercial HVAC systems.
The room doors are akin to residential exterior doors, sealed all round for weather but you'll be buying something similar (and NOT undercut) for sound abatement & STC raaings. Even a small hole lets in plenty of sound.
Next comes the new room RA registers ... perhaps with fiters ... sized, fitted, installed by your HVAC company and their calculations.
However, even with heavily insulated new ductwork, sound will travel from room-room via these air tunnels; some mitigation of noises occur when "white noise" air is rushing through the ducts. Adding more duct turns may mitigation further.

A second solution less fancy, perhaps less quiet may be to simply tune your HVAC system - if needed - hand-in-hand with your HVAC Co
then add white noise fans to the homework rooms, finding the ideal location, perhaps near the closed doors ... which HVAC Co may advise to undercut further?
Those that have sleeping problems will also buy white noise machines, EZ to get on Amazon/local shops.

Caveat: it's best to avoid things that leak such as added ductwork unless the system was installed poorly

Love to hear the solution that worked best for you later!