My brother pass away we want to open his iPhone but don’t know his password

This is the process to ask for access to someone’s data -> How to request access to a deceased family member's Apple accounts - Apple Support

But please note that Apple cannot unlock a screen locked iPhone. They have no means to do that. Nobody does.

From that article linked above: “Please note that devices locked with a passcode are protected by passcode encryption, and unless the next of kin knows the device passcode, Apple will not be able to remove the passcode lock on the device without erasing it.”

You can remove the passcode of the iPhone by following these steps https://support.apple.com/en-us/HT204306 but in doing that it will reset all the data as well