Ownership right of basement

Hi, All are equal right in the property, you can divide the property by mutual understanding amongest yourself.

2. All the brothers have 1/4 th undived share in the land of the property.

basement would form part of common areas for benefit of all the flat owners 

All the 4 brothers have equal undivided share in the land and one building is constructed they will equally divided the share in the land lying beneath as well in the constructed portion.
However to avoid any future dispute I would recommend you to go for amicable partition so there is no animosity as regards respective possession and enjoyment.

This can be jointly decided by the brothers by executing a family settlement. The current owner of ground floor can agree to pass the title of it to any of his brothers. 

Hi
 all four will have  equal right unless there is an agreement stating the ownership of the said  stilt parking & basement .
If there is an agreement or registered deed pertaining to the ownership which is stating the ownership of the property to any one or a person other than you four, then  all four will have an easement right for use an occupation.
The right depends on the kind of ownership and title  you four have on the building and the land beneath it.

basement can be used for benefit of all members provided you have permission of muncipal corporation for the same 

By way of an agreement you can build anything on the basement.

Hi we are 4 brothers planning to reconstruct the building with 4 floors , stilt parking & basement on a 500 sq yard plot
i want to know who will have the ownership of basement? will it be the person who owns the ground floor currently or does all the persons have a equall right on it?

This can be agreed on mutual agreement of the shareholders.  However, since it involves parking space and other common areas, it shall be be utilised in common by all the owners.

Also I wanted to know that  can we use basement for building a swimming pool, home theatre etc
as i told plot area is more than 550 square yards located in  west delhi.

The proposed swimming pool or mini cinema hall is again a common decision.  If all the shareholders agree for the common amenities, they can get the plan approved by the competent authority sanctioning the said proposals.