The “Backlog refinement” activity (not team) is a chance for PO and the developer team to come to the same page and so explain about / ask for the details before thinking that story is ready for sprint (backlog) planning and for estimation of story points. The “Product backlog refinement team” should aim at this same goal as well.
Therefore, in my opinion, they should:
- not deal with story points, and leave them for planning;
- not throw out anything (PO will select/order), just ask about them in order to understand requirement much more;
- expand the US with all new aspects and information helping to understand the US much more;
- explain if the US is too big and so it should be divided smaller stories.
Hope it helps.