Land mapping............

In Maharashtra, if the Tehsildar’s map is missing, you must stop searching for the visual map (Nakasha) and instead apply to the Taluka Inspector of Land Records (TILR) for the "Tippan" (field measurement book) and "Phalani" (subdivision data). These technical documents contain the raw mathematical measurements of your land and can be used to legally reconstruct boundaries even without a drawing. If the Land Records office refuses to survey based on these, your most effective remedy is to file a Civil Suit and invoke Order 26 Rule 9 of the CPC, asking the judge to appoint the TILR as a Court Commissioner; this court order legally compels the department to retrieve archived records (potentially from the Settlement Commissioner in Pune) and demarcate your land, bypassing the local administrative deadlock.

To immediately stop your co-sharer from encroaching upon the unpartitioned land, the most crucial and urgent step is to file a Civil Suit for Injunction and simultaneously move an application under Order 39, Rules 1 and 2 of the Civil Procedure Code (CPC).

Approach concerned Tehsildar for demarcation.

It is better to seek professional services of a local prudent lawyer practicing revenue matters.

You submit an application to get the property surveyed through government surveyor by paying the fees after which you can get to know the details of the owners of the property.

Then you can go for partition.

When doing a partition, why is some land unpartitioned? Post facts.

Yes, the fasts posted lack clarity and too vague to offer any meaningful suggestion.