SalamOne day at my grandmother's house, a chador became najis by me. The najasat was such, that it could not transfer to any any other object. So, I did not tell anyone about that najasat and returned the chador as it is. My question is that is that Wajib on me to tell them( my relatives at my grandmother's house) that the chador has become najis by me?thank you

Walaikumussalam
Yes it is wajib on you to make it Pak now please inform them and ask them to do Taharat.
Wassalam