Scope of BCMS

You do not need to include all the functions in the Organisation to go for ISO 22301 certification.

The best approach would be to define the BCMS scope in terms of the products and/or services you provide, and from the nature of each one of them identify which functions should be included in the BCMS. In case you have multiple divisions and locations, you should consider independent certifications, so any problem in one site cannot impact the certification of other sites.

This article is related to ISMS but can provide some tips about defining a BCMS scope:

• How to define the ISMS scope https://advisera.com/27001academy/knowledgebase/how-to-define-the-isms-scope/

These materials will also help you regarding BCMS scope definition:

• Book Becoming Resilient, The Definitive Guide to ISO 22301 Implementation  https://advisera.com/books/becoming-resilient-the-definitive-guide-to-iso-22301-implementation/ 
• Free online training ISO 22301: An overview of the BCM implementation process https://advisera.com/27001academy/webinars/