If you are referring to the need for auditors to be certified, then no, there is no specified need to be certiifed. Internal Auditors need to be competent to perform internal audits for their facility, meaning have the depth of knowledge and understanding of the purpose of ISO 17025, and have auditing know-how and soft skills on approaching lab personnel.
If you are asking if you need both lead and other auditors, then again, this is not a mandatory reuirement. In a large laboratory there may be teams of internal auditors and then it makes sense to have a lead of the audit team. This person typically plans the audit with the Quality Manager as per the programme (schedule) and ensures that the team has suitable resources (such as the correct checklists and audit scope). It does not necessarily mean that they perform the management audit components as performed by a lead assessor of an accreditation body. arrangements all depend on the size of your laboratory and the competency of available personnel to perform internal audits. In a large laboratory having lead auditors to do the management (non technical) audits is a practical arrangement for efficiency.
The following will provide more information on Internal Audits: