HI Robert,
Good Luck with your exam, please let's know when you are done so that we congratulate you on the success
below are my thoughts regarding your questions:
1- In real life, project managers don't have the authority to terminate projects. we can only suggest such action with the implications of such decisions. PMO has the authority to take such decisions and this is aligned with the PMBOK (check section 1.4.4 Project Management Office "
A PMO may have the authority to act as an integral stakeholder and a key decision maker throughout the life of each project, to make recommendations, or to terminate projects or take other actions, as required, to remain aligned with the business objectives").
2,3- the project charter main objective is "
to authorize the existence of a project", it also documents the main objectives, assumptions, contstarints and the high level understanding of the product. the project charter is a main input to the planning activities. after that the main reference is the project management plan not the charter, and as for the PMBOK it is not stated any where that it gets updated in any process.