When a project manager realizes that some stakeholders are working against the success targets of the project, it's important to engage all stakeholders, including the unsupportive ones. This is because every stakeholder has a role to play in the project, and their concerns need to be addressed for the project to succeed.
The project manager should also update the project stakeholder analysis and methods to satisfy the stakeholders' requirements. This involves identifying the needs and expectations of the stakeholders and developing strategies to meet them. By doing so, the project manager can ensure that the stakeholders are satisfied and that their concerns are addressed, which can lead to their support for the project.
While escalating the issue to the functional manager (option B), involving all stakeholders by distributing status reports (option C), and focusing on the supportive stakeholders (option D) might be part of the subsequent actions, the immediate steps should be to engage all stakeholders and update the stakeholder analysis and methods.
: Project Management Body of Knowledge (PMBOK) Guide, 6th Edition, Section 13: Stakeholder Management.