Is it the case(as I believe) that modern double glazing window units can be fully installed from inside the building? I am on third floor so wondering about need for scaffolding.
It's perfectly possible to remove an old window and fit a new one in its place. The difficulty I can see would finishing off around the outside of the frame. Even if the fit is perfect, it's usual to put a silicone seal around the window to finish it off.
All I can think of is to remove the opening casements so that you can lean out to get at the reveals. Not an option though if you have a fixed pane on one side.
Agree on that.
If they are timber casements, you may be able to reach to seal depending on width of the frame. With any type you could seal a certain amount from inside apertures whilst installing tho.
Regarding any type, if they are subject to driving rain, etc, you really need to seal up properly.
Most modern UPVC double glazed windows are glazed from the inside for security reasons these days. It should be easy enough to seal the outside of the frame to the brickwork with a standard silicone sealant gun before fitting the glass.