Yes, you definitely can help your realtive buy a house in the Bay Area - I have a few clients who do that differently (on title, gifts (which has a limit) , none gifts, etc).
Let me know if you need a mortgage broker to give you more details (I am a Realtor and will not be able to give you all the detailed, up to date information about how to get the loan for situation like yours.
On the other hand, if you're paying the mortgage and not an owner... you are technically a renter and can't claim home ownership related deductions. But again, please consult a tax professional for tax questions. If you want to start a home search try http://www.automated-homefinder.com