I am not a lawyer so cannot provide the answers that you need. You need to consult an Indian lawyer who understands the complexities of both international law and of liability in healthcare.
The legal issues surrounding medical tourism are complex. e.g.
If you are a medical tourism agency, and you send a patient to a hospital and the operation goes badly wrong, what is your liability?
Will the patient sue you, or the hospital, or the doctor....or all three? Where will you be sued? If the patient is from the UK, the lawyers may choose to sue you in the UK courts rather than the indian courts.
>>>Do we need to register with some authority to bring patients from abroad.???
There is no registration or licensing system for medical tourism. There are various certification and best practice systems that you might consider, including the Treatment Abroad Code of Practice for Medical Tourism.