Upvote:2
As per Timatic, they are entitled to TWOV (transit without visa) if they do not leave the airport:
Destination - Bangladesh (BD)
Passport
Passport required.
Document Validity:
Passports and other documents accepted for entry must be valid on arrival. Admission and Transit Restrictions: Passengers with a handwritten passport are not allowed to enter. Warning: Passengers with a handwritten extension on a machine readable passport are not allowed to enter Bangladesh.
Transit - India (IN)
Visa
Visa required.
TWOV (Transit Without Visa):
Passengers with a confirmed onward ticket for a flight to a third country within 24 hours. They must stay in the international transit area of the airport and have documents required for the next destination.
Additional Information:
Holders of visas that specifically state the city/airport of entry must enter India at the specified city/airport. Hotel facilities are available in Terminal 3 at Delhi (DEL) for passengers with a boarding pass for their connecting flight.