You could plant a tree or two in the garden, and while that wouldn't solve the overlooking problem immediately, it might eventually.
I would use the study as a fourth bedroom, rather than trying to carve up the lounge. As long as whoever slept in the study wouldn't mind people tiptoeing through to the bathroom that might work. I think the kitchen diner is too small to use as a permanent lounge. You would all be tripping all over each other all the time.
Maybe carve off a small study from the front of the lounge if you need a study/office/craft/junk storage space? It could be accessible through the lounge.
What would put me off is the sterile look of the whole place, beginning with the brick and gravel front. However, that could be remedied with plants. It cries out for a nice creeper/vine imo.
As for parking I see the carport opens into the garden any chance of building a garage where the shed is, sort of an extension of the carport, and whoever has to be out first in the morning parks closest to the street...
I would say four agents means the owner needs to sell.