passwords

Which one works when logging in?

Only one should work. If you created a user, and the changed the password for it, then only the current password would work.

If you have 2 users for the same website, then each user would have its own password.

If one of them does not work, then the password is not updated from the last time you changed it. You may need to turn on iCloud Keychain to have the password list sync between devices. Also, both devices need to be using the same Apple ID in System Preferences ➜ Apple ID.

Click here ➜ Set up iCloud Keychain - Apple Support

Not the same as what?

Each website should have its own password. You shouldn't use the same password for different bank websites.

Why is it a problem exactly?

Explain your issue in as much detail as possible, and someone may be able to advise.