That yourname comes only second, is immaterial.
It is presumed that as per the PURCHASE DEED, you have half right in the property, and that the property is used for the owners' own residence. If so,
- you can claim 50 % of the interest on the Housing Loan, provided you are also a borrower
- as you are already claiming Rs 1lakh under S 80C, you can't claim further deduction in respect of your share of the Stamp Duty paid.