We bought a house with in-laws. We got a quick claim deed but are not on the mortgage, can we deduct half of the interest and how do we do that?

So long as you are on the title, whether through quit claim or warranty deed, you can deduct the mortgage interest that you pay.

(Editorial:  It's one of my hang ups, but it's a quit claim deed.  There is no such thing as a quick claim deed.)