The phone will need to be reset – which will wipe out all of the data on the phone, as muguy said. However, there might still be a possibility for saving photos and other data. This depends on them existing in some location other than just the phone.
The greatest chance of there being up-to-date data to recover would be if your brother had automatic backups to iCloud enabled, and/or was synchronizing some kinds of data (like photos) to iCloud. Then the phone would have been automatically copying data to iCloud, and there might be fairly up-to-date data in iCloud that would survive the reset of the phone.
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If your brother was using iCloud Photos, many or all of the photos and videos on his phone might also be in iCloud. They could be accessed by synchronizing another device to iCloud Photos (with his Apple ID and password) or by logging into the iCloud Web interface (https://www.icloud.com/) with his Apple ID and password.
If your brother was not using iCloud Photos, the photos and videos might be in a backup of his phone. There is no good way to see what is in an iPhone backup without restoring it.
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You will probably need to gain access to your brother's Apple Account. The steps for doing that are outlined here.
How to request access to a deceased family member’s Apple Account - Apple Support
The person who makes the request might need to be the court-appointed executor or administrator.
