Are the doors and windows common property in a 1970s building?
With the exception of your fire rated front door, I suspect they aren’t, in which case I would be sending them an email saying that you have made every effort to consult with them and due to their lack of engagement you are going to go ahead and change the windows and balcony doors, albeit with due consideration for the look of the building.
If they are common property, tell them that you intend to take them to Fair Trading for mediation, followed by seeking orders at NCAT under Section 232 (2), compelling them to fix all the windows in the building.
I would add a rider saying you apologise for the firmness of tone but they have a duty of care and that involves discussing and negotiating with owners over matters related to common property.