Undivided share among co owners can be made sole ownership to each other

Dear Legal advisors, I have bought a vacant land having an extent of 800 square feet together with 50% undivided share and interest in common passage (corresponds to106 sq.feet). Altogether having an extent of 906 sq feet (800 sq feet + 106 sq ft undivided share in common passage). The seller who sold me told that I am the sole owner for 106 sq feet and to the passage which is next to my vacant site and the person who lives behind my vacant site is the sole owner for the other side 50% in common passage. But there is no mention of side or dimension of this 50% of undivided share in common passage in the sale deed (whether its horizontal or vertical split) . So my title to that 106 square feet is ambigous. Now the person who owns the other 50% says that we will register a deed saying that the split is vertical and that I am the sole owner for 50% in passage which is next to my 800 sq ft property and he for rest 50% next to his land there is road in front of both our properties and this passage is of no use to either of us. Please advice if we both co owners enter into a sale deed and make sole owner for that passage as we both have 50% undivided share to each of us and add an amendment or rectification deed specifying that we are the sole owners for 106? Thanks, Chandra.