You cannot claim him because you have not paid more than half of his total support for the year - the state has.
Also, claiming the mortgage deduction is not related to your being able to claim him. To claim the mortgage interest you must be legally obligate to pay it with you either being on the mortgage contract or the property title.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
