I would use allot of WD-40 or deep penetrating break free oil to get down and loosen the rust and stuff.
What you do not want to do is to put too much muscle in to this project and do some rounding off of the think the pipe wrench grabs onto. This will make the project impossible.
If you can get a socket or something on the thing to eliminate the possiblilty of slippage, this would be great. Rent a truckers socket wrench with the appropriate socket and then get a small pipe cheater and try that along with the penetrating oils.
If its safe, and I mean safe, try alittle heat on the area.
They will come off, but this is more mind than muscle.