If I get my 12 word phrase, what are the odds someone else gets it too? Is it easier to add a pass phrase?
If you generate seed words randomly, correctly and offline, using standard words and backing them up in safe place, there is no chance someone else could guess them or unlock anything.
There is however always a chance you made a mistake with leaking your words or someone could steal them from you and spend your bitcoin.
The pass phrase will just make it that much harder to unlock the bitcoin right?
Adding a passphrase is like adding a salt that adds extra layer of protection, but only if you keep it safe and separate from your seed words, this adds more complexity and more security.
You can have multiple passphrases but keeping them all together with backup phrase makes them useless.