Karlson beautifully took care of the international aspect of this situation wherein unfortunately you cannot carry a kirpan as carry-on on yourself.

But, since Mr.Sardarji is a religious person and it is possible that he would like to make his family happy without making sacrifices with his beliefs I would like to provide more information with regard to the kirpan and how it can be carried on some flights.

As this question of Sikh Answers explains,

The Kirpan (Punjabi: ਕਿਰਪਾਨ, kirpān) is a religious sword worn in a strap that enables a it to be suspended near one’s waist or tucked inside one’s belt. A Sikh who wears a kirpan is not wearing it because it is a weapon; he or she is wearing it because it is part of their officially prescribed religious uniform.

The kirpan usually looks something like this,

As you can see the object is relatively small and Air India (as well as Jet Airways, it seems it's a regulation everyone must follow) does allow it in domestic flights,

As long as one can assure that the blade size is less than 6 inches and the total size of the object is less than 9 inches. This provision is specifically for the kirpan and is mentioned specifically in the rules for hand luggage as well.

A 'Kirpan' with a total maximum length of 9 inches (22.86 cms.), but a blade not exceeding 06 (six) inches (15.24 cms.), is permitted for carriage by a Sikh Passenger on his person, within India or on an Indian Registered aircraft on Domestic routes of fully Domestic Flights within India, subject to the requirement of a Public Order. (BCAS Circular 14/2005).

But unfortunately to conform with international regulations, they also cannot allow it on international flights,

Carriage of ‘Kirpan’ shall not be permitted in the cabin of an aircraft on an International Flight, either on the domestic or international sector flown by the passenger. If the 'Kirpan' is more than the length specified above, it shall be carried by the passenger in his registered baggage.

So my suggestion to Mr.Sardarji,

You can try to convince your family to take a flight to somewhere else in India which can be far from Punjab (India is a big country after all, full of culture!) and still carry your kirpan with you. Maybe if you and your family sit together and talk, you all can reach a suitable decision.