My back of the envelope calculations would suggest that the interest on your loan is less than the rent.
Not sure there is enough benefit from any exotic arrangements.
Especially as inter family arrangements get LOTS of scutiny[quite rightly] from ATO and centerlink.
Whether you pay off the loan quickly, probably depends on what else you might want to use the money for.
Getting rid of any non deductable debt first, usually worthwhile.
Are you planning to live in this place yourself at some time in the future?
