There are various restrictions on booking rewards flights with Air India India Maharaja club.
First of all, you need to complete two paid flights on Air India and these should have been tagged with your member ID. Secondly, you need to create a family pool by adding other family members. The members to be added need their own Maharaja Club accounts and these accounts must be at least 2 years old. Then, you need to email Air India to add them to the family pool and they need to provide their consent. Then and only then, you can book reward flights for them