If your fingerprint scanner is based on simple ridge profiles, then it's shouldn't be used for security. For example, some recent Apple keynotes claim they now use sub-dermal features for identification.

Implementation matters more than what the sensor is authing with.

What if we did something like a mix of password + finger print, by using multiple fingers in a pattern?

Like, say, middle - index - ring.

It would be doubly unique.

It would be more unique but it would take away the convenience of having your phone unlocked nearly instantly with your finger. If you're going by security, a password plus fingerprint would be most secure but inconvenient.