If you want to know who attacks your Shipmates without asking them about it each time, you can set up the incoming battle reports about the attacks on your Shipmates' Havens. You will be receiving the battle reports after all incoming attacks, scouts and blockades of their Havens.
Such option is available for all players in the game. However, it can be activated only if both sides configure the incoming battle reports of the Shipmates. Such option can be found at the Envoy's Reports settings. When you open the settings you will find two tabs: My reports and Shipmates' reports. At the Shipmates' reports tab you have to select friends who will be receiving the battle reports about your Haven. Your Shipmates need to do the same if you want to receive their battle reports. Please note that you will not be getting the Shipmates' reports until they select you at their Envoy's settings.
Now when the Shipmates have been selected, please go to "My reports" tab and mark the types of the reports you would like to receive. Do not forget to Save the changes when the selection is done. From now on you will be receiving the notifications about interactions with your Shipmates' Havens.