By default, only 5 fingerprints can be added to the iPhone with Touch ID. This is a software limitation.
However, not all of this is enough for one reason or another. There is a way to expand this amount to 10.
How to do it
1 . Go to Settings -> Touch ID and passcode .
2 . Enter your iPhone password and click Add Fingerprint .
3 . Apply two fingers instead of one to the Home button.
This way you can add two fingerprints at once in one scan. And in total, their number will increase from five to ten. Checked works .
Note that this will decrease the scan accuracy slightly.