One policy for all: this is the idea of a multi-person household. As the name suggests, all persons living in the same household are insured with the same benefits. The premium per person is thus slightly cheaper than for a single-person household. The prerequisite for this is that all persons are registered with the authorities at the same address.
This option is recommended for shared flats where people know each other well, have similar insurance needs and plan to live together for a longer period of time.