1. Yes, they have equal rights,

2. the cost for making the 1F will be borne by the C&D

C and D have inherited B 50 per cent share in property 

2) on redevelopment C and D would have equal rights as A 

It seems that c and d are the legal shares of B and will get share from share they got from  heritance so the decision of property will be held according to the partition deed between A and B.

They shall have equal rights in the redevelopment as per there share. 

Dear Sir,

It all depends upon family settlement if any or Will if any or as per Sections 8 and 15 of Indian Successions Act if they belongs to Hindu religion.

Since A and B had their rights in the property the rights of B have been automatically transferred to C and D  by way of the testamentary disposition made in their favor by B.

Therefore C and D combined inherit the rights of B which is equal to the rights of A in the structure  respectively as well as in the land beneath the structure.

A and B have 50% share each in land. And C and D can have 25% each of B share. So if G and 1F constructed than C N D have half share in F1.

C and D will have rights what B had and will be equally divided

C & D  have equal rights, If there is no will.

1. Since "B" is the owner of 1F, the legal heirs (C & D) are legally entitled to unrestricted rights & title-ownership over 1F and ALL subsequent developments /reconstructions /benefits accruing (to the extent of 1F).

2. Rights of C & D would be restricted /limited to the Area ratio of 1F and not on the Area ratio of G.  Hence IF area of G is more then 1F, THEN "C & D" shall not be entitled to any benefit accruing out of area of G.

They will inherit complete share of B which is 50% of total property.