You cannot legally download a single file containing 1268 episodes. What you can do is stream the Tamil version legally, episode by episode, on Disney+ Hotstar (under the title "Mahabharat Tamil")—though they may have consolidated episodes into a smaller number.
Very difficult. Some fan archives on Internet Archive have partial collections, but most are incomplete. You cannot legally download a single file containing
If you prefer a physical copy for permanent ownership, various retailers offer the complete series in Tamil: episode by episode