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The easiest option is to go to a quality parts store such as NAPA, Bumper2Bumper, Carquest, and purchase a special socket that has reverse raised spiral edges designed to remove rounded bolts, locking lug nuts. You hammer the socket over the lug nut and use an extension and ratchet to loosen and remove them
Here is sample of what the socket looks like. This is one I personally use made by OTC($40):
They come as a flip socket in 2 sizes 19/21mm, 21/23 mm, etc. Drive your vehicle to the parts store to match up the correct socket.
2 other methods-
Sorry, the rest of your post didnt show up until I had already posted my answer on removing the wheel lock. The brackets that hold the windows are only available thru an Isuzu dealership, or possbily thru a salvage yard. There isnt any aftermarket companies that make them Below is the national used part locater. You simply put in the the year, make, and model, and then select the part you are looking for, and your zipcode. If there is one available at a salvage yard near you, it will show you the name of the salvage yard, location, phone number and price of part: