my face id isn’t good… it’s unlocked by my brother face also without setting with his face

While not impossible it’s still quite rare; even for siblings.

I’d suggest that you reset your FaceID - saving new images of ONLY your face when you’re alone AND change your passcode to something only YOU know.

Then see if your brother can still unlock your device.

If he can … you’re a statistical anomaly … stop using FaceID if your brother is around.

(keep in mind that repeatedly entering a passcode while in public carries it’s own significant security risks - using a long custom numeric passcode mitigates this risk while still being easy for you to enter)

If he can’t … don’t share your passcode with him again. 🤔

First reset your Face ID.

Another thing to note is that Face ID will continue to update if your face is not detected and requires you entering your passcode. This is to enable continued use even after you change your appearance such as glasses, makeup or other facial features. If your brother uses your phone a lot by entering your passcode, it will start to recognize features of his face as well. The solution is to disable Face ID or stop your brother from using your phone by entering your passcode if you want to continue to use the Face ID feature.