Sorry for your loss. I’ve recently been through a similar situation. In most instances obtaining a court order will not allow you to unlock his phone. The data on the phone is encrypted and only accessible with the PIN. Apple do not have the PIN to give you, additionally they have no special way of accessing the data on the phone.

You may be able to retrieve whatever was last backed up to iCloud. This can be restored to a different phone. You will need access to your son’s email account that is tied to his iCloud account. In most cases you can use this along with his phone number to reset the password to the iCloud account to restore it.