How to safeguard my property?

Around 30 years back I've kept my property papers in the bank locker along with some jewellery and handovered the keys to my son. Locker is in the joint name with my son. Since then I never asked him about the locker keys or the property papers. But now my son has passed away and I asked my grandson about the bank locker keys, firstly he showed trantrums and later gave me and told that my son had opened one new locker in another bank but grandson has no information what my son has taken out from previous locker and what is kept in new one. When I opened my locker, it was empty. Nothing was there. And my grandson hasn't cleared me whether property papers are with them or not. He is lingering on by giving an excuse that I can't open new locker because it's in papa's name and death certificate is still in process to come which is needed for the bank formalities. So, now I doubt whether they have misused the property papers or will they sale it out or change the name. Now what should I do to protect my house and livelihood? What actions should be taken?