Firstly, let’s establish the era of your Double Hung Sash Windows.
Are they Art Deco 1920s? Federation style or Victorian or Colonial?
Okay... let’s make it easier... most sash windows in the Sydney area pre 1950 are Counterbalance Double Hung Sash Windows with a rope and pulley system. If you have these windows they are made of quality joinery and cedar frames and hardwood sills.