Indian revenue property records explanation needed?

What is the difference between 7/12 extract, 8a extract, and 6 Hak Patra?

If one’s names as owners are on 6 Hak Patra, but not on 7/12 extract what are the legal implications?

If a property owner dies leaving heirs such as wife and children, what do they need to do to enter their names on the revenue records, i.e. what is the procedure and what documents would they need to furnish to enter their names on record?

Thank you , this is very important, so only serious replies please from knowledgeable people.