Face ID recognition security issue

Hello~ Does your brother have access to your iPhone and your Apple ID? If so rescan your face when he is nowhere around and change your Apple ID password and then see if his face unlocks your device.

Set up Face ID on iPhone - Apple Support

Change your Apple ID password - Apple Support

If at this point it still happens you need to take your iPhone and your brother in to Apple store and demonstrate this to them

Genius Bar Reservation and Apple Support Options

~Katana-San~

See this Apple support article→About Face ID advanced technology - Apple Support, specifically:

The probability that a random person in the population could look at your iPhone or iPad Pro and unlock it using Face ID is approximately 1 in 1,000,000 with a single enrolled appearance. As an additional protection, Face ID allows only five unsuccessful match attempts before a passcode is required. The statistical probability is different for twins and siblings that look like you and among children under the age of 13, because their distinct facial features may not have fully developed. If you're concerned about this, we recommend using a passcode to authenticate.

Hey Suryate, sorry you are having this issue.

Please make sure Face ID is set up properly, to do this follow the instructions in this article:

https://support.apple.com/guide/iphone/set-up-face-id-iph6d162927a/ios

Hope this helps, have a great day!

-Kyle