Are test labs required to have certified lead and internal auditors as a requirement for ISO 17025 Assessment?

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:

How to perform an internal audit using ISO 19011 at https://info.advisera.com/free-download/how-to-perform-an-internal-audit-using-iso-19011
ISO 17025 document template: Internal Audit Procedure at https://advisera.com/17025academy/documentation/internal-audit-procedure/
The Five Internal Audit Procedure appendices Internal Audit Program, Internal Audit Checklist, Audit Nonconformity Report, Internal Audit Process Checklist and Internal Audit Report are available separately from the procedure link above; or included in the toolkit at https://advisera.com/17025academy/iso-17025-documentation-toolkit/
Clause-by-clause explanation of ISO 17025:2017 at https://info.advisera.com/17025academy/free-download/clause-by-clause-explanation-of-iso-17025/
Book - ISO internal audit: A plain English guide at https://advisera.com/books/iso-internal-audit-plain-english-guide/