Who is responsible for ordering the Product Backlog?

A new software development team has just been formed. 5 sprints have passed and the team is now familiar with their way of working. In the 6th sprint, the scrum master notices the team members arguing about the technical design of an upcoming new feature during a backlogrefinement meeting. After the refinement meeting, the scrum master notices team members talking about the topic informally and taking sides. There is noticeable tension among the team. How should the scrum master help the team to resolve the issue?

A new project is scheduled to begin next month. The project manager has had plenty of time to review and plan all the activities and has adopted the best approach for the project and the organization. Which action did the project manager most likely take when choosing the approach?

What Agile requirements management approach displays a roadmap using the following approach? The horizontal axis shows a high level overview of the system under development and the value it adds to the users.
The vertical axis organizes detailed stories into releases according to importance, priority, etc.

At a strategic level, what is the most appropriate way for an Agile team to estimate a project?