Tenanted Flat in the name of Grand Father
Cost of Acquisition: Not Known
Acquired by Grandfather  in the year Prior to 1961
Grand Father Expired in the Year 1972
Permanent Alternate Accommodation Agreement (PAAA) Between My Father (Only Legal Heir) and Land Owner cum Developer registered on 26.12.2013
Value of the flat as per Stamp duty Authority as on 26.12.2013  was Rs. 12.86 Lakhs
Condition in PAAA: Tenancy Will Surrender only on receipt of possession New flat on Ownership Basis
My Father Expired on : 07.01.2018
Full OC received on  : 25.03.2021
Possession of new flat on ownership basis handed over to Legal Heirs on 26.05.2021
New flat sold  on 12.08.2021
Sales Consideration 65 Lakhs

Query:

1. Taxation of Capital gain in which Year and also Whether it is short term or Long considering in the hands of Legal Heirs considering
   Transfer U/s.2(47)(v) section 45 of IT Act and Section 53A of TOPA and Section 45(5A) effective from AY 2018-2019
2. Any benefit of Indexation and also exemption u/s.54 available new flat available on surrender of tenancy rights.

Pls share your valuable opinion.

Thanks and Regards