If the sill plates are bent from decay or structural failure then you have real problems and even if they're not a 9 ton concentrated load or a 9 ton distributed load will bend a 4x4 that is not uniformly supported by the ground.
This thing should be raised by at least three jacks with one at the corner. But, if you sight along the sill plates and they're high in the middle it's the corners where the soil has subsided.
Since there's no drywall you can see everything and make a pretty good estimate of the weight of this structure.
A default value for the density of softwood is 35 lbs/cu ft. How many pieces of what length and width and depth are there?
As to cause, maybe you can find it here