No pipe wrenches, the way they grip the nuts actually crushes them to the axle if you put too much pressure on them, it destroys the nuts and it makes them even tighter.
Go to harbor freight and get an 18" adjustable wrench, about 25 bucks and it works better than any tool they sell designed for axle nuts. Have somebody sit on the quad and hold the brake pedal to keep it from rolling forward, and give a good lift on it with that big adjustable wrench, i've never tried that and not have it work. If it's still stubborn, get a propane torch and heat up the nuts good for a few minutes, and try it again. Heat will cause the metal to expand, loosening them on the axle.