When two devices are set up for the same person, both are linked to a single user. In this case, one device is designated as the primary and the other as the secondary.
Messages and reminders are delivered only to the primary device. This is done to avoid duplication and prevent overwhelming the user with the same information on both devices.
Despite this, both devices can be used to send messages to family members normally. The difference is only in receiving messages and reminders, which are centralized on the primary device.