You will need to screw out the adjusters and retap the holes. Soak with some penetrant spray and let it sit over night. Try working the adjuster back and forth. If necessary use some heat from a heat gun or torch. If you use the torch be careful not to use too much heat or set the car on fire. Heat the backing plate where the adjusting wedges screw in, not the adjusting wedges.
The wrench sold by the vendors for adjusting the brakes will give you some additional leverage.
Once the adjusters are moving, remove the shoes and screw the adjusters all the way in so that they pop off the dust caps inside the brakes and continuing to screw them in until they come out.
Buy or borrow a tap to rethread the holes. I forget what size the tap should be, but take one adjuster to the hardware store to get the tap.
Put a thin coating of grease or anti seize on the threads and reinstall the adjusting wedges. Reinstall the dust caps using a socket wrench and peen over the edge of the hole that they go into in a couple of places to keep them in place.