Generally (Used to be) in the united states the social worker will present the general ethical frameworks to reason within and it is up to family to provide the answer. Ethics boards develop recommendations as needed, when courts have to step in.
I will say working in a Trauma and ICU rooms, families are generally well aware of the decisions to be made when it is time.
They are assigned a triage score and that score will be updated routinely. As beds open, the people who fit the criteria get the bed. I believe that is fairly standard in a public hospital type setting.
I have only ever worked in public and military icu, wards, er and trauma rooms so I do not know too many details on how that works in practice.
I will say working in a Trauma and ICU rooms, families are generally well aware of the decisions to be made when it is time.