1.Your First Question what will happen to the housing loan? First, you go to your bank ask them to provide you outstanding loan amount and a list of documents (docs) you submitted to the bank when you taking the loan like sale agreement, NOC, share certificate, etc).
Suppose your loan outstanding is Rs.10 lacs ( this 10 lacs mean only principal outstanding and any delay EMI fee etc, the bank will not take interest to remember only ask for principle outstanding )and selling in Rs.30 lacks .in this situation you have to pay Rs.10 lacs to the bank and recover all original documents.
if your purchaser buying your house by a loan he/she can take a loan from the same bank in this situation documents bank can easily transfer to his/her loan. or he/she taking a loan from any other bank, then either you pay the entire outstanding loan and recover/collect all documents you gave to the bank at the time of taking a loan, a second option called seller BT in this situation Purchaser bank provide outstanding amount to your bank to close your loan and collect all your documents from your bank if any balance you have to receive from purchaser your seller will give you after collecting all documents, including sale deed made between you and purchaser and NOC.
2.You can not transfer your loan to a purchaser or transfer your loan, only he/she can apply for a fresh loan. internal transfer of loan to others not valid.