Links are not allowed according to the terms and conditions
Be that as it may:
Have you actually read through your links?
It explicitly refers to a granny flat (by the way with a separate entrance and kitchen) which will then serve various purposes in the future...
But that requires exactly this separately built granny flat, which you will not build initially, as you have told us, but only one or two generations later.
Hmm, why are 2 ventilation systems necessary? We have a shared technical room, but only 1 ventilation and 1 heating system, probably with separate meters, supply lines, etc. But no one wanted to install a second unit.