The aluminum windows in the bedrooms sweat water especially at night and in the winter. I know it is moisture in the air. The plaster around the windowsill needs to be replaced. Should I put another material on them then seal them, or is there a product I can paint the aluminum with so it won't be so cold ? The window is open at night and the door is closed. The house is 40 years old.
Your problem is ventilation. If you do not have bathroom and kitchen exhaust fans please have them installed. You should always leave the exhaust fans on for 1 hour (minimum) after each shower, bathing, cooking etc. If you have a summer switch on the furnace fan leave it on for a couple of days to air out your home. Leave a window upstairs open a 2” crack when the summer fan is on.