Hello Barry,
if you manage the subprojects via a Master project file, you should have a resource project pool.
You must open the resource project not in "read only option" but in "read-write option", so you can make changes to resource information.
After opening the resource project, click in "project" tab and then in "change working time": now you can planning the company Holiday setting the non-workings days in the base calendar.
Ensure to save the file when you close it: when you'll open a subproject file, you should view the changes.
Regards
Codeghi