Education loan

My son as an applicant has applied for Education Loan to pursue higher studies in USA. My self is co-borrower. I have two querries: 1.AS co-borrower how much rebate I get for interest paid in last year AY2017-18 for Education Loan. 2.Can my wife also become 2nd co-borrower for son's primary loan account. Can my wife also claim interest for Education Loan, if wife pays interest for Education Loan form her account to son's account? 3. Is it necessary for my wife to be 2nd co-borrower to claim for tax rebate for interest paid for education loan by her for son's higher education loan.