No it isn't. What they are asking for would quite possibly leave a bigger carbon footprint than not doing it would, and is also both impossible and impractical to achieve when we can't even mass build new homes that are carbon neutral, and have a housing shortage.
Creating, transporting and using materials emits carbon. A lot of it. And you can't just shove a bit of insulation into an 80 year old home which will have a multitude of other issues in relation to energy efficiency (not least cold bridging areas in the construction which would render extra insulation somewhat pointless) and expect it to make a big difference.
The answer is going to be in either how energy is provided to these homes (wind, solar), or a revolutionary way being developed to build new homes that are carbon neutral, that is efficient enough to allow old homes to be replaced (doesn't exist yet).
The problem with these protests is exactly this. Protesting about something you don't even have an answer for and are too lazy to research properly is completely fecking pointless.
I'd be right on board if their proposals had any ounce of sense, but they might as well be protesting for the government to fly them all to Mars in a hot air balloon.
At the moment the government can't even get developers to build new housing as energy efficient as it should be, so maybe they should be protesting about that instead of something completely self defeating?