Best method to record self-declaration by wife on family issues

Dear Sir, My wife is willing to provide self-declaration via Affidavit/notary or other accepted legal method regarding few facts about her life and marriage. She wants to ensure that if anything happens to her or us so this can be used as recorded evidence in case any false legal action to me or her where we have no time to provide any statement. Kindly advise the best way to proceed. 1. Is self-declaration on white paper are sufficient? 2. Should we get an affidavit or notary? If what is procedure. Facts: 1. There was no dowry exchanged or demanded during the Marriage. However financial condition of her family was not good at time of marriage and they had requested my help and I paid them Rs. 2 Lakh which they never refunded. I am a professional and earning in six figure so had no issues with money but they cheated me. You can say that in other word they have taken dowry from Boy. 2. She wants to declare that she is very happy staying with me and getting all support and there has been no domestic violence or any sort of torture after marriage that anyone can blame as we fear. 3. There has been multiple cases where her family members forced her for monetary support after marriage. She has paid big cash to her family without my knowledge. Her family demanding that I should transfer my property ownership to my wife so they get chance to force and misuse. Which means they can also do anything to me. 4. She is very much concerned about our safety but she does not want to go against them now or to report however she is willing to provide written declaration to me and in case anything happens then this can be used to protect my dignity and from any false legal issues in court. 5. She went through deep depression before Marriage since childhood due to lack of family support. She was kept as maid servant to support her family on everything from domestic work to providing maid service to their Brother-in-law house for years and was not allowed to marry until age of 32.5 until his father died and I said yes to proposal immediately but they were not ready and giving all reason not proceed with marriage. Though she had no other issue with her personality and also carrying master’s degree. She was also wanted to pursue higher education but was not supported by her family which I fulfilled. 6. Her family is very educated and has strong financial support now but they are greedy and we fear can do anything and go through false legal action even there is no evident since there is law made to protect boy in case of Marriage issues. But my wife understands that and she would like to protect us from such damage. Please help. Thanks in advance. Regards, Kumar N