Proof of authority under local law that you are the lawful representative of the deceased person or their estate
Note: Instagram will never let you log into the deceased person’s account. It's always against the Instagram Policies to log into another person's account.
However, despite it being a violation of the terms and conditions, some people recommend that you can reset the password for the account and log in. This could work if you already have access to your loved one’s email, phone, or Facebook account. We are not endorsing this choice, but if recommended by your lawyer, here are the instructions:
Open the Instagram App
On the login screen, tap “Get help signing in”
On Android: select Username or Email, Send an SMS or Log In with Facebook, then enter the information and follow the on-screen instructions
On iOS, tap Username or Phone. Enter the email address, username or phone number, then tap Send Login Link.