Your OP says you have a set of air bags in a context that they are there to carry load. It says you want to add two more because you carry HEAVY load.
After several replies, you come back and say you have Kelderman Air Ride.
I can tell you not a single person is going to take your first post and figure anything OTHER than air bags over the axle. Kelderman is nothing close to that. Kelderman is not designed to increase load by even a single pound. They are designed to ride on air while the truck is empty so you don't have a harsh ride.
I've never heard of 'em, had to look 'em up;
https://kelderman.com/shop/1994-2002-ram-2500-3500-2-stage-rear-air-suspension-longbox
Photo shows, the rear shackle is replaced with an air bag. No extra capacity for load, strictly for a smoother ride when empty.