Multiple Scrum Teams shared between multiple POs

The existence of multiple Product Owners implies multiple products, each with their own Product Backlog. If a Scrum Team is working with multiple Product Owners, then that implies that the Scrum Team is working on multiple products.

If the team is attempting to work on multiple products within the same Sprint, that leads to a lack of focus. It is unlikely that a team is able to craft a cohesive Sprint Goal.

Even if the team is working on one product at a time, there is likely to be contention over what product the team will be working on. This contention may prevent the team from being committed to stakeholders and a Product Goal.

In short: I don't think that it works. It may "work" for some sense of the word for some organizations, but it's not an ideal situation.

The norm is that a product has a single PB and a single PO, with one or more scrum teams. 

Yes, a scrum team does include a PO; however, when a product has multiple scrum teams, there will only be one PO who is moved into the integration team, as a product should only have one PO. 

A PO could in theory be accountable for more than one product; however, this should be determined by that POs capacity, as being a PO is usually a full time job, so a PO having multiple products could be seen be some as not being focused enough. 

How does sharing multiple scrum teams between multiple POs work?

Each Product should have exactly one Product Backlog with exactly one Product Owner. This helps to assure accountability and transparency. If team members are shared across teams and/or products, they ought to respect this principle, and take any losses due to context-switching and reduced focus into account.

How does sharing multiple scrum teams between multiple POs work?

I believe the real question is does it work? Think about the scrum teams' ability to commit and focus (two Scrum values) if their work is split across multiple areas.  The Scrum Guide defines a Scrum Team as 

The fundamental unit of Scrum is a small team of people, a Scrum Team. The Scrum Team consists of one Scrum Master, one Product Owner, and Developers. Within a Scrum Team, there are no sub-teams or hierarchies. It is a cohesive unit of professionals focused on one objective at a time, the Product Goal.

Notice the words "share" or "multiple" are not in that description.  True the word "Developers" is plural but the statement of "one Product Owner" indicates that there is a single point of ownership of work definition. 

Could a single Scrum Master or Product Owner work on multiple teams? Sure they can and I have done so.  But the Developers on the teams were singularly focused on work described by the single Product Backlog which was maintained by a single Product Owner.  The Scrum Teams were not shared between multiple Product Owners.  They shared a common Product Backlog but each Sprint was done completely independently of any other Scrum Teams working out of that same Product Backlog.