Hi,
All the tires carry 'about' the same weight. Now the outside passenger side tire can sometimes sit out in free air, when you are 'really close' to the shoulder of the road. I have also watched a big rig towing a 45' trailer, and get to close to the curb, and put the outside dual tires on a curb, so that the inside tire was up in the air, over the hitch.
The dual tires are rated for less than the normal weight rating of a 215/80R16 tire. I think that mine are rated at 2700 single and 2,450 dual, or 4900 total for each side.
Probably you will not have more than about 2,000 pounds per tire, except for extreme towing. . .
Fred.