Pinkbunny and Smitha:
Here's how things worked for my wife and I, with maybe too much information, but maybe some of it will be helpful. Our twins were born at about 33 weeks in October '14 (like a lot of people, we got the out of the blue "come now!" e-mail). Our kids were born at around 4 and a half pounds, maybe a little less, and neither had to be on ventilators. I don't know how things have changed due to the new facilities, but our kids were cared for at the Zydrus hospital, which I found to be excellent on the whole (modern, clean, doctors I felt confidence in), though there were a couple of cultural surprises. Our daughter stayed in the NICU for about 4 days, our son for perhaps 8, and then we stayed with them in the hospital for about another week. Zydrus has suites you can rent that are a lot nicer than staying at the Rama, though I missed the room service. Nurses (or "sisters" as they are called there) in and our every couple of hours to check on things and help out, which was a comfort to new parents like us. Depending on when your kids are born you may have a longer or shorter stay.
We weren't sure about flying at 2 weeks to Mumbai. The doctor was hedging a bit, and stated at one point they had to be 2.5 kilos to be allowed by the airline to fly, though no one ever asked us their weight when we did eventually fly. We actually hired Uday, the local fixer who works with Dr. Patel, to drive us to Mumbai--I forget the exact amount, but it did not break the bank by American transportation standards. There is also a train available, though we weren't comfortable taking that. This was something like a 7-8 hour trip as I recall, and went fine.
We had to bring the babies back to Anand to get exit visas. We made a real effort to try to convince the Mumbai FFRO office that the regulations gave them authority to issue the visas, but they wouldn't budge. The process was very frustrating--the police commissioner in Anand, the one man empowered to give us the visas, was on vacation, and we had a hard time getting straight answers from anyone as to what our options were. Uday ultimately arranged things somehow. We flew the kids back to Anand when they were almost or about 4 weeks old, handled the exit visas in one day, spent the night at the Rama, and flew back to Mumbai the next morning. We then flew to Newark a couple of days later, and it wasn't a problem for the kids. They were actually remarkably well behaved, and didn't seem bothered by the flight at all.
Some morals of the story, and other tips that wouldn't be obvious:
unless there's been some policy change, you're going to have to bring your babies back to Anand. The stress we had in trying to find some way to avoid this was a lot worse than the actual trip back to Anand.
a lot of your problems can be solved by giving money to Uday. I didn't ask questions as to where it was going, and how much he kept. Completely worth it.
We found dealing with the bureaucracy to be a nightmare, but that was largely because we tried to buck the system and get them to do things that made sense. If you a) accept you're going back to Anand and b) give Uday money, it will be a lot less stressful.
If you are told to give your babies preemie formula (the local brand was called Pre-Nan as I recall), buy a ton of it at Zydrus or at Dr. Patel's new facility if available. We had a really hard time finding it in Mumbai.
Order a bunch of "original" copies of the birth certificates (I'd say at least 5), but check them very carefully when you get them, as they will have mistakes and need to be redone. Be sure to check the gender is correct. There's a separate fixer who handles birth certificates, and if it's getting close to when you plan to go to Mumbai you'll want to keep some pressure on to make sure you get them in time.
When you have a sense of when you'll be able to get to Mumbai, don't forget to go online and schedule your consular appointment and DNA test---you can schedule them to take place one after the other, which I recommend. The DNA folks take their samples at the consulate, but don't forget to go the day before to the DNA lab's office to pay for the testing. I forgot to do this last bit, and had to race the clock to get them their payment before their fedex deadline to make sure they'd send the samples to the lab prior to the upcoming weekend.
Be aware that the holiday Diwali is coming up in early November, which makes booking hotels and the like harder.
Anyway, the Drs. Patel an Uday know what they're doing, and you'll get through it. Good luck!