1. Deed of confirmation is not a registered sale deed or a title deed.
A confirmation deed means assent to the estate already created. By the confirmation, the parties further strengthen and give legal validity to the estate. A person may confirm and assent documents of conveyance executed by another person. ... Also, a copy of the principal deed should be annexed to the deed of confirmation.
It may so happen that a party to a document has made a mistake while signing the main document or has failed to admit the execution before the sub-registrar within the prescribed time. As such, a sub-registrar may refuse to register the document. Or else the parties may have executed the documents, but failed to register at a sub-registrar’s office to admit execution, and the registering authority may refuse to register the document. In order to remedy these defects, a deed of confirmation has to be executed by the party concerned, where he confirms the execution of principal deed and further adds that the principal deed is valid and binding on him. He also confirms that he has no right, interest, or title to the property transferred which belongs to the purchaser/transferee. Also, a copy of the principal deed should be annexed to the deed of confirmation. The copy should also be signed by the party executing the confirmation deed. This avoids execution of fresh documents, payment of stamp duty and registration charges.
2. There is no necessity to pay the stamp duty again if it has already been paid.
3. Yes, you can do that, you may go through the first answer above.
4. The seller will be liable for payment of income tax as per his income and also for LTCG or STCG as applicable.