As a general rule, the whole team is responsible for breaking down the epics prior to implementing them. It's fine to put the epic in the backlog and prioritize it, and then break it down just before the iteration in which it is planned for implementation. When breaking it down, the product owner (or other customer and user representatives) would help to identify the subprocesses of the epic so that it can be broken down into its constituent parts.
However, without an understanding of the problem domain or the requirements of the system, I'm not sure how the development team can have a conversation with the product owner, customers, and users about what they are delivering. Depending on the complexity of the problem domain, they might not have an in-depth understanding, but I would expect some kind of education about the customer's business and domain-specific terminology, the problems the system is trying to solve, and the general direction and high-level requirements of the system under development for everyone involved in the project.