Fortunately mine came right out, no fuss. You will need to persuade them to loosen up.
Have you tried copious amounts of penetrating oil yet? If not, try it! If that doesn't work I'd try using a propane torch to heat them up really good (be careful of fire!), then bash them with a BFH while hot to see if it losens the rust.
Then, if all else fails bring out the big guns- torch and/ or cutoff device.