The purpose of a project brief in PRINCE2 is to provide a full and firm foundation for the initiation of the project. It includes information necessary to decide whether or not to initiate the project and acts as a base document against which the project board and key stakeholders can assess project progress during its lifecycle. References: PRINCE2 Foundation Handbook, Project Brief section.

Both statements about stakeholders are true in the context of PRINCE2. A stakeholder in a project includes anyone who thinks they will be affected by the project, which can include both supporters and those who may oppose the project. Additionally, stakeholders can be both internal and external to the organization that is undertaking the project. References: PRINCE2 Foundation official documentation and study materials.