here is the site plan
What are the blue lines - the distance of the carports from the street? (that looks like about 5m)
that I find it hard to imagine a house where a granny flat has 80 sqm on the ground floor and the main house about 70 sqm on the ground floor and 90 sqm above. What roof shape would be suitable for that.
So 80+70 = 150 sqm ground floor total would quite accurately yield 90 sqm in the roof above both, with a gable roof.
It is supposed not to look like a duplex. The granny flat should be inconspicuous.
If both conditions are to be met, you can't put them next to each other like a garage.
Besides, the above calculation fits "classically" like a glove, and any deviation would lead to contortions to make it fit again.
You can plaster one part and brick the other (or vice versa) and much more.