Legal value of notarised document and sell deed

I purchased a flat from my sister in Jan 2016, but court affixed an order (dated Sep 2016) on Door in the month of Feb 2018 that she (my sister) can’t sell that flat to anyone. Main matter is, my sister has taken Rs. 11 Lac without any interest in 2011 (as next party is saying), she (sister) had given cheque to next party, also a notarized document (Year 2011) (not registered) that if she is unable to repay Rs. 11 Lac within 6 months, next party can sell the flat and can get their money. I was unaware of all this. I trusted my sister that’s why not gone for search report or newspaper adv. I have paid some amount in cash and some NEFT Transfers to my sister and paid her home loan through RTGS. Next party saying I did fake sell deed, so that they can’t get money. My registered sell deed is be4 the notice date. My question is, is there any value of only notarized document after such a long period? Is it necessary to get search report before purchasing the property? What could be result?