I wonder that when and how we can be failed for this audit?
Best preventive action about that is to perform some demanding internal audits in order to check the current situation and prepare people for the certification audit
How many major Finding, minor finding Auditor found that make us have to re-audit again?
That will depend from certification body to certification body. Normally, If one organization gets one major nonconformity, it cannot be certified before the audit team confirms that the nonconformity can be closed. If that confirmation can only be seen on site, a follow-up audit will be needed before certification.
About the number of minor nonconformities that can be accepted without requiring a follow-up audit before certification, that will depend from certification to certification body.
You can find more information in the following links: