Co applicant in home loan

nephew can have wife.  how he has a husband?

Family Court has nothing to do in this case which is clearly commercial transaction between your nephew and husband of your niece (if I'm not wrong). The nephew can write to the HDFC Bank about his moving out of the agreement of purchase of the property for which he became co-borrower of the bank loan. He can even send the similar letter to the seller of the property, the registrar office or tehsil office about his discontinuation of the sale agreement as co-owner of the property in question.