How much money am I allowed to exchange at the airport in India?

There is no limit generally, but at your time of travel there will very likely be one, imposed by the individual exchange agencies due to lack of supply. Cash is in extremely short supply all over India these days. It's actually possible that you'll be unable to get any Indian Rupees at all at the airport. And if you do, long lines and amount limits at the counter are not unlikely. For more details, see "India just demonetized all Rs 500 & 1000 notes. What do I do with my leftover cash?" and "How can I exchange Rs 500 & 1000 notes in India as a foreigner?".

Such a limit would be per person. Since you are a large group, you could divide the money between each of you, and all get in line together. That would take longer and possibly incur more exchange fees, but it may be worth it if you can get the desired amount of cash for your trip. India is still largely cash-based, and there's a great lot you do need cash for.

If you end up having to exchange with third parties outside the airport, please note that there are two occasional scams going on in that business these days.

1. People trying to sell you the old 500 and 1000 notes. These are almost useless to you now, so stay away from them.
2. There are fake versions of the new 500 and 2000 notes circulating. The criminals printing and circulating these are taking advantage of the fact that they are still somewhat rare and many people don't know that well exactly what they look like.

So be aware of those dangers. Also, it's normal to get a somewhat low exchange rate these days. Some of my friends had to settle for 10% below mid-market rates due to the low supply of rupees and the seller's market that has lead to.