https://www.desidime.com/discussions/airtel-second-dth-connection?page=1#post_8267404
if it is same building, then you can get 4 connections by same antenna. 899rs was the charges for hd box few months ago, not sure now. No additional installation charge. You need to pay extra monthly for the plan whatever you choose.
Here one benefit, minimum monthly amount is around 61rs (if no plan selected and only free channel opted), compared to 153rs in case of separate individual connection.