On first point, that is an excellent advice to the OP. Its much better to go with that option but he'd have to prove the relationship and the fact that they are sick (Doctor's note would suffice).

On your question, all you need is to find a doctor in India, have him/her write up a formal letter addressing to "Whomever it may concern" and make sure they include your full name and address and basically spell out why it would be medically necessary for you to travel to India so they can provide you the services. I would try to get them to include details on how they provide those services and you would be the right patient. Try to stay away from the financial related narrative.

I went to India on my first time for humanitarian reasons, during that visit I had an eye procedure done, so for my second time I used medical reason (follow-up lol). But yes I had a full proof doctor's note proving it all.