"Company has both certificates 9001 and 13485. There was only one internal audit, not divided depend of ISO number. The question is either internal auditor needs to have certificates for both ISO or only one, because both ISO is for Quality Management."
Auditors should dominate the audit criteria used.
ISO 13485 includes the entire ISO 9001 standard with additional requirements.
So, your organization’s internal auditors can have ISO 13485 awareness training or can have ISO 9001 awareness training with an additional module about what is specific of ISO 13485.
Remember, organizations have the authority to define internal auditor competence requirements.