How to save myself from false blame

H,ble sir/madam, 1. I am retired from defence, presently working in Mumbai. 2. My brother-in-law requested me for a suitable match for his only son. His son is educated and working. Financial condition of my brother in law is also quite sound. 3. Hence, I requested my own sister and her husband to marry their daughter to my brother in law son. The same is arranged one year before. Mandatory to note that financial condition of my sister is weak. 4. Problem now are as hereunder (a) My brother in law and his wife complain that the girl, married to their son act differently, her action feels like she is psychiatric. She starts wiping her bed and house hold items, if any one touches. She does not eat despite repeated instruction and going weak day by day. They also complaint that for any silly reason she talks to her mother i.e. my sister 5 to 6 times in a day. She acts as per instructions as per her mother (my sister). My brother in law and his wife also complaint that their son is fully supporting his wife and neglecting them. (b) When I tried to discuss thus matter to my sister and her husband, I was astonished hearing her reply. She said that all the member in the family is wrong and her daughter is right. She clearly told me that if anything goes wrong I shall be held responsible. 5. Sir/madam, after studying all corner, I can only say that my sister interference has increased and she is unable to understand that one should not interfere in family life of one's daughter. Apart from that my brother in law and his wife has only son and they do not want to allow their son and his wife to live separately in same town. 6. The girl activity shows that she may have some psycho problem, but her husband is not accepting. In case anything goes wrong I do not want to get involve in all these matters. Kindly advice me what step should I take at my end to save my selves. Sincere thanks Amar nath Ojha