They would live in rented property, only the company that owned it would be their company so owning it would be by default surely?
So it's essentially a common or garden tax dodge; A nice house with a garden full of gnomes, paid for legitimately with no real abuse of trust.
I wouldn't question that, simply because it's not abusing a position of trust. It is not encumbent on a citizen to maximise his taxation obligations.
It is, however, up to an MP to minimise his expenses which are taken from funds raised by taxation.