i am a fraternal twin and me and my sister can unlock each others phone using facial recognition.

That is not a breach. Apple has said since Face ID was announced that close family members would be able to unlock devices. Your best security is to not let each other near your devices. If you do not trust your own sister with your device that is not something we as fellow users can solve. You can turn off Face ID and use a passcode if you are that concerned.

About Face ID advanced technology - Apple Support

The OP has already been given an answer for their situation. Rebuking them is not necessary.

No. You should have known that, Apple even said that when they revealed Face ID with the iPhone X. Looks like you need turn Face ID off and use a Passcode, or get an iPhone with Touch ID.