Considering that at DEL (as is common in India) one must show a boarding pass to armed guards in order to enter the terminal, I wonder if those involved were some form of staff at the airport. It is extremely difficult for non-passengers to enter the terminal, let alone for that number of times.

The other scenario could be at the arrivals area which can be very busy with meet and greets, etc. But again, for people to be there for that length of time and that frequency it leads me to wonder if they were some sort of staff.