"My grandfather is my friend."
Translation:मेरे दादा जी मेरे दोस्त हैं।
I think it’s like this: to show respect, the word ‘grandfather’ is used as if it were plural. Now consider something else that is plural instead of grandfather, for example sisters.
In English you would say “my sisters are my friends”. Notice that friendS and not friend is used. Friend is in plural because the word ‘sisters’ is plural
So in the same way, since grandfather is sort of considered plural to show him respect, I think it should be treated as a plural word as well, just like sisters.
I hope this makes sense. I’m not 100% sure this is the right explanation but it’s my idea of it.