Tax implication on selling ownership rights

Hi,

My grandma was having a pagdhi house approx. 140 sq.ft carpet area since 1975 , last year landlord has enter into the agreement  to redeveloped the property and in return would give a 225 sq.ft carpet area on ownership basis by 2019. Now my grandma wants to sell her ownership rights but the property is not yet redeveloped it would get developed by 2019.

My question is :

1. Whether my grandma can sell her ownership rights even if the property is not yet developed by entering into an agreement with the buyer.
2. What would be the tax implication since in surrendering/ transferring tenancy rights cost of acquisition has to be taken nil, but once the property is redeveloped and ownership property is handed over by landlord cost of acquisition can be taken as current market value when ownership possession is handed. What cost of acquisition would be in this case?
3. How the stamp duty would get calculate whether it should be calculated on the basis of 140 sq.ft or 225 sq.ft. and it should be calculated of which year 2017 or 2019 when property gets develpoed and registeration is done.
4. Whether it would be consider as long term capital gain or short term.

Thanks