Dear Mr. Kannan,
I agree with Mr.Adinath. You should file a suit for partition and declaration and file the unregistered document as a Deed of Family Arrangement (which need not be registered). Thereafter, you can prove the partition through the parties to the document.
Alternatively, if all the parties to the document are alive, you can get all of them to execute a fresh Deed of Partition and register the same in which you can mention that the parties have already divided the properties as per the unregistered Family Arrangement and the prsent deed is being executed to confirm the same.
Thanks, Ramakrishnan, ADV