As a guy who lives in a 7x5m studio somewhere in Eastern Europ, in a building like this one http://farm4.staticflickr.com/3152/3082829290_9653703b1e_b.j..., I try and try again to find out why would you need three bathrooms and five bedrooms, but I really cannot think of any reasons.
My parents have 5 children, and while now their house is way too big for their needs, it was not the case when me and all my siblings lived with them.