Get a mapp gas torch and heat the outer one. Get two good big adjustable wrenches. Put the tires back on heat the nut again. And place one wrench on the inner nut and against the ground. Put the other longer one on and give it hell. I've had to use a pipe to do itbefore


If that doesn't work take a cut off wheel and cut in about half to 3/4 way through and smack it good with a sharp chisel that should break it. Once the outer one is off the inner should come off relatively easy. Then just get a new nut.