If you know the brand of windows, I would first make contact with the manufacturer and see if they have local recommended service people. You want someone that is familiar with your windows and the "tricks" necessary to get them back into satisfactory working order. If you don't know the manufacturer, contact a local shop/lumberyard that deals with different brands and they may have their own people. I would send them pictures as well. Sounds like the windows are racked but a 1/2" is a large gap. It might be something else.