The availability distribution of a group is based on the average availability of all the members present in the specific group for 24 hours.
A group cannot be created in the following cases:
No, a combination of devices and interfaces cannot be grouped together as both of them have entirely different properties. But a device group (group containing devices) and interface group (group containing interfaces) can be placed under one subgroup.
You can add group members automatically to a group during discovery by creating a group with criteria. Please note that in future, during network discovery or when adding a device, if any of the devices or interfaces discovered match the criteria specified in the group criteria, then those devices or interfaces will be automatically added to that group.