My husband uses heat for too-tight pedals. He drags out a blow torch, like the kind Martha Stewart uses to make creme brulee, and just heats up the connection, then has another go. It usually works. Be sure to clean and then lube the parts before putting them back together.
(First make sure you are turning them the right way)
If all else fails I use an 18" section of 1" inside diameter gas pipe that I use for setting crown races and put the handle of the pedal wrench part way inside it for extra leverage. Never fails.
Just to reiterate the previous post: make sure you are going the right way. I stripped one of my pedals b/c I didn’t realize that one side is reverse threaded.