The ordering guarantees are as follows:

If Subscriber A is subscribed to both Topic 1 and Topic 2, and Publisher B first publishes an Event 1 to Topic 1and then an Event 2 to Topic 2, then Subscriber A will first receive Event 1 and then Event 2. This also holds if Topic 1 and Topic 2 are identical.

In other words, WAMP guarantees ordering of events between any given pair of Publisher and Subscriber.

Further, if Subscriber A subscribes to Topic 1, the SUBSCRIBED message will be sent by the Broker to Subscriber A before any EVENT message for Topic 1.

There is no guarantee regarding the order of return for multiple subsequent subscribe requests. A subscribe request might require the Broker to do a time-consuming lookup in some database, whereas another subscribe request second might be permissible immediately.

The WAMP protocol requires a subscription to be shared amogst subscribers to the same topic.

A subscription is created when a client sends a subscription request for a topic where there are currently no other subscribers. It is deleted when the last subscriber cancels its subscriptions, or its session is disconnected.

A subscriber receives a subscription ID as the result of a successful subscription request. When an second subscriber issues a subscription request for the same topic, then it receives the same subscription ID.

The WAMP protocol is not clear on whether a registration ID is shared or nor amongst multiple Callees registering the same URI under the shared registration feature.

According to section 14.3.7.1.3.5. the call to wamp.registration.list_callees(RegistrationId)retrieves a list of session IDs for sessions currently attached to the registration, which implies all Callees shared the same RegistrationId. Crossbar.io documentation says the same.