Thank You Bryanna for your reply. But I have one doubt. My father is 81 years old and does not know English. We are from Kerala, the southwestern state of India and need to take minimum three flights to reach Calgary. How can they complete the PR landing formalities in Calgary without knowing English. So I wonder why my purpose of visit is not a valid one. Please reply.
Agreed. The language barrier is not a valid reason to accompany your parents.
Here's a solution for your parents:
1. You can accompany your parents on a domestic flight from Kerala to Mumbai/Chennai. This would eliminate one unaccompanied flight + you can help them to change between the domestic and international airports especially in Mumbai. That said, do keep in mind the luggage allowance for domestic flights.
2. I would not recommend flying out of Trivandrum. That would mean spending time at another domestic airport like Mumbai/Delhi before the onward flights to Calgary.
3. You may want to consider flights with a layover in HKG. Don't consider flights that transit through the US because your parents will need US visas for that transit.
4. Do keep in mind: Your parents would need to complete their landing formalities at the first airport they land in Canada. Depending on their flight bookings, this could most probably be Vancouver, unless they fly non-stop from Mumbai to Toronto Pearson. Landing formalities will not be at Calgary.
5. Airline staff are happy to help. Your dad can request for wheelchair assistance even if he is medically fit. It would save the efforts of walking
6. Your parents must carry a letter that explains that they do not know English + that they need to complete PR landing formalities