What do you mean by having all his other information? The only information you need is the Apple ID and Password for the device. Activation Lock is the measure put in place to prevent others from using a device that is not theirs.
Apple will only unlock devices, when the original owner submits the receipt from Apple or Authorized Apple seller showing their name and serial number of the device.
How to remove Activation Lock - Apple Support
Or, if a Family member has passed away, they can submit legal documentation that may include court records to have the lock removed.
How to request access to a deceased family member's Apple account - Apple Support