NRI's Property in India (Mortgage & Family Issues)

Hi. My father was an Indian citizen till 2008 and has been another Asian country's citizen ever since. He has some land and a house in India much before that in joint ownership with his wife (who is still an Indian Citizen by living outside India). Ever since our family migrated here, he has been in some financial mishaps and wanted to sell the house and land in India. This was not possible as his elder brother and his family had moved in to stay in the house to take care of his(and my father's) mother. They have been living there for quite a few years now. So when my father expressed his wish to sell the house, he was in a way influenced to place the house on mortgage for some 25 lakhs. The brother had also arranged money on his own to help my father too. Unfortunately, the arrangement didn't really help my father's situation. The understanding at that point was for my father to send money to India to handle the mortgage installments and gradually give back what the brother took for him too. If I understand correctly, the brother had taken loans from a legal creditor (not a banking institution) to help my father too. My father couldn't really keep up with the monthly installments; he had things to take care of here(where we are at now) which were equally if not more crucial. At different points along these years, my father had repeatedly told them that he would like to sell the house but it was never really accepted. It was like they had usurped the house. I understand my father was/is also at fault for not sending the monthly installments(which they have been handling themselves) for some time now too which has put the brother's whole family in distress too. It is not fair to them at all. So they had reached an understanding where the brother wanted to buy the house(which according to my mother was their plan always). The idea was to deduct all what my father owes the banks(so the brother will take care of the installments) and to his brother and if there is anything outstanding,then my father is to pay it back gradually over a period. My father is not in a position to go back to India and had agreed that he will sign the house in their name the next time he In order to process this, apparently (I have never been involved in the interaction and only know what my father has told us) my father was asked to send in documents. What baffles my father (And quite honestly me) is how they are asking for his foreign passport and foreign identification card. Isn't his Indian documents necessary for him to sell a house in India that he got when he was an Indian? Plus maybe his OCI even can be given but are his foreign documents necessary? There has been a lot of friction and emotional turmoil because of this in our family and between my father and his brother it is very exhausting. He is not in a state to get professional lawyers to advice him either so I am hoping this helps. Thank you in advance, kind lawyers.