Income from HP

Mr. X owns a house with 100% ownership and treated as SOP (property A) . Mr. X and Mr. Y (son of Mr. X) own another property in 50% ratio (property B). Property B is SOP of Mr. Y. My query is whether Mr. X should declare his share in property B as deemed let-out and pay tax or he need not? Both, father and son, pay 50% of housing loan from their respective bank account. Whether Mr. X can claimh his share of interest payment and repayment of principal amount agaist property B? Please give references.