Lab signatures

You asked

is it possible to exclude the lab manager from the signature and add only the lab managers?

Yes, this may be possible. Because forms are documents - meaning they are formatted to contain information that will be filled and become a record;  all forms must be controlled as per your document control procedure. ISO 17025 does not prescribe who has to sign and how many signatures there needs to be. It is the laboratory's responsibility to consider the risk and to what extent your documents need to be managed.  The purpose is to ensure the forms are designed with the correct fields in order to obtain and retain meaningful, required information. Typically, a document has an author (subject knowledgeable or expert), a reviewer (subject knowledgeable or expert), and an approver (authorizer). The reviewer and approver (authorizer) may even be the same person.

For more information on document control, see the ISO 17025 toolkit document template: Document and Record Control Procedure at https://advisera.com/17025academy/documentation/document-and-record-control-procedure.