Relative not clearing loan for which i m guarantor

Dear Sir/Madam, We have a piece of land in the name of my mother. About 10 yrs back, one of our relatives needed financial assistance to start his business, he asked us to help him by becoming guarantor for a loan he is seeking from a bank. Since he was one of our relatives, we decided to help him to be a guarantor for his loan, he took loan against that piece of land which is in my mother's name. Primarily he maintained the CC account well. But soon he got married and his business failed to survive. During the first 1-3 years after taking loan, he got married, built a house, he shut down his business and started land brooking. Now we have learnt that, he also owns a car too. Now my family wants to built a house on that land, but since there is a loan against the land, we are afraid in doing so. We have repeatedly reminded him to clear all his loan so that, the plot is freed and we can built house. But today about 10 years after the loan sanction, he always makes excuses about clearing the loan amount. Now we think water is flowing over our head. So we seek legal assistance/advice on this topic as per the following points. 1. My mother is illiterate, they took my mother to bank and took her thumb impressions wherever required for the loan: please tell me what are rules, if an illiterate woman is becoming guarantor for a loan, I mean is it necessary for a literate family member to be present during such procedures, which involves an illiterate woman from family. Is the procedure legal? 2. Can we still built house on the land? As the cost of materials are rising as hell, and we are afraid, with time it will go on increasing, which will lead to rise in estimated built up cost for the house. 3. Since the person has sound property, is it possible for us to go and claim the same in the court/bank so that, the loan amount is transferred to the person’s property. Please help. Thanking you in anticipation