option B is the best option, its better for smaller groups of players and small clans and will basically create a second type of port battle that can be called when people want to fight and not later this is good for regular players and people who don't like the politics and frontlines.
having a flag that you need to bring to a city to announce a raid is also a very good idea, I can still remember the great battles I and my clan/ nation got while using or countering this mechanic. basically, if option b is chosen a raid will hopefully bring more action and interesting situations to NA and will tempt some regular players to come back to the game.
however, there is 1 issue, after the raid is completed the loot should not be capturable or only half of it so that a big nation cant just gank a smaller nation that is raiding, perhaps a special slot on ships should be created in which players can put the loot that they think is most valuable so after the raid is successful the attackers did the whole raid for nothing. there is also the other side of the story, for instance, I could also imagine that a raiding nation would not go into the raid without backup from there allies and the attacking nation should think of battle plans and what to do when the defending nation just blockades the port and waits for the raiders to go back home with there loot.
also, it wasn't fully clear to me if the attacking nation is only battling against elite NPCs, I would prefer to fight players and only if the attackers lack players the slots will be filled with NPC after a few minutes as in reinforces.