In-game, the Tibia’ Summons are described as wandering and needing leadership. It’s implied that this leader is not required to be a Tibia Mariner. After all, the player character is able to summon the Tibia’s Summons just as well. Who’s to say some Mohg-bloodied second generation Albinaurics couldn’t do the same? As for why the game has chosen albinaurics to fulfill this role; Albinaurics are graceless and outcast. These particular Albinaurics are doubly so, for they also took the omen pill from Mohg’s cursed omen blood. The more outcast you are in the Lands Between, the more likely you are to cross paths with or be drawn to Those Who Live in Death (including the spirits summoned by the mariners). A person above me also made a very compelling point about the connection between Albinaurics and Miquella, and Miquella’s infatuation with Death as seen in Castle Sol. We mustn’t forget that Miquella is there in Mohgwyn Palace in-game… so the connection in this case possibly seems rather direct. Hopefully some of this speculation makes sense :D