We can combine one-way and bidirectional replication in the same network. If you created the map family on London Office Portal, then it would be replicated to Corporate Office Portal. Corporate Office Portal has two outbound connections that belong to the same group; ensuring changes made on Corporate Office Portal are replicated to both Extranet Portal and back to London Office Portal.
Since the Extranet to Corporate connection does not belong to the group, changes made on Extranet are not replicated back to Corporate Office Portal.
Each pair of web applications must have two Replication Connections. Replication Connections specify how one web application will talk to the other and also ensure each web application is authorized to communicate with the other.
As SharePoint content is being replicated between web applications, the Replicator instances for each web application are actively communicating with each other and delivering status updates. This is why each web application in a pair must have an outbound and an inbound connection to the other web application.
Map families define what SharePoint changes will be automatically replicated and how often that replication will occur. In most cases, there is only one map family defined for a Replication Network, but there are also valid reasons for having multiple map families.
When you create a map family, you specify its scope. The scope determines which events are available to capture. You should select the scope of your map family to represent the events you want to capture. For example if you want to capture and replicate new site collections, then you must create your map family with a Web Application scope.
Queuing and capturing are two different ways in which SharePoint events are replicated.