How do I unlock deceased family member's iPhone passcode?

I am sorry for your loss.

You will need to follow the directions in this link to get Apple to help you --> How to request access to a deceased family member’s Apple Account - Apple Support

Typically this means you'll need a death certificate and a document from the estate granting ownership rights to the device. Apple will likely NOT give you access to the data on the phone. With the proper documentation, they will usually wipe the device to let a new user use the device.

Sorry, but you don't. The best you can do, is request access to his Apple ID, and restore the device.

Without the passcode, you cannot get into the iPad in any way.

Once restored, and with access to his Apple Account, you can then restore a backup if one is available to get the data back.

click here ➜ How to request access to a deceased family member’s Apple Account - Apple Support

click here ➜ If you forgot your iPhone passcode or your iPhone is disabled - Apple Support

How to request access to a deceased family member’s Apple Account - Apple Support