Neighbor stole will and claiming the property

My school teacher died 3 months back who use to stay alone. He made an affidavit against his daughter and spouse few years back which states that they would not claim or have share in this particular flat directly or indirectly which was signed by them. Now when he died his neighbor took possession of his flat with a claim that before his death, few years back he borrowed 25 lacs against the flat by keeping his original will, affidavit and all the relevant documents with him. The value of this property is 35 lacs. He is in a process of selling it off and doesn't wish to share it