Heat the nuts with a propane torch, fairly not, and allow to cool prior to the attempt.

Once the nut barely moves............add much more PB or Kroil............and keep working the nut back and forth...........repeatedly............about 200 times..........to allow the PB to work into the threads. Do not attempt to continue removal until the nut is moving decently for a full 360 degrees.

Did I mention to keep spraying that PB........or Kroil........

Patience is a virtue.