Note*** : My solution is for one pair of wheel. I don't know if it goes along with the ambiguous requirement "Axle solution for one pair of wheels".
I know this is what most people will end up with. I've not inovate in any ways, but I still think it is the best way to do this. It's very straight foward, it has 2 major parts to produce (laser cut and metal folding) and some fasteners. No welding.
*A spacer could be added (blue part on render 4).
*Note that on the renders the shock should be on the other side (the side where the leaf spring is sliding, not the pivot side)