It is not fixed, it is a live artifact that will grow and change as more is learnt. The product owner orders it by value.

Scrum doesn't know any other role than developer. The developers are cross-functional and have all the skills needed to create a usable increment. They are doing the work and responsible for the architecture.

there is no project plan, the presence of stakeholders in the development area is probably not helping and there is no project management. Transparancy would avoid the surprise for the stakeholders. If the PO didn't frequently update them, this can also lead to surprise and disappointent. If the stakeholders couldn't attend the sprint review they would also not be up to date and missing out on an opportunity to inspect and adapt.

Pair programming means that two developers are coding together and performing live peer review. This will enhance the effectivity as it leads to increased code quality. Regardless of your opinion, when answering Question:s about pair programming, know that it's considered a really good practice for PSD. And in case you are wondering, the instructor of the course is also a big fan.

If you are not sure, please review the section scrum artifacts in the scrum guide.