I'll begin with the easiest aspect: physical appearance. In the entire game, I was only able to find four people with blue hair and blue eyes: Erik, his sister Mia, the Seer, and Morcant. Erik's hair is a frequently noted part of his appearance, notably in the Echo Chamber's rendition of Weaver's Peak, and when afflicted with Shypox.
Now I'll look at the connections between these characters and the region of Sniflheim. During the course of the story, we find that Erik and his sister are orphans, with no known family beyond each other, and their Viking guardians/employers/masters. Beyond this, we know that they have lived in the Sniflheim region for most of their lives, having acquired the regional accent. It is possible, though not 100% certain, that they are native to this region.
Morcant has strong ties to the Sniflheim region himself. Having been the original mage to seal away Krystalinda in the Witch's Tome, he is an important figure of legend there. Books relating to magical power that he wrote can be found in the nearby Royal Library, as well as his own personal study. According to Snorri, and a book in Snifleheim Palace, the kingdom was founded by scholars and intellectuals making use of the Royal Library. Morcant is revealed to be of noble birth, with sufficient wealth and power, it may be possible that Morcant's family are tied to the scholars that founded Sniflheim, and are also based in this region. Obviously, considering Morcant's fate, it is highly unlikely that Erik and Mia are his direct descendants, instead being connected to the family he left behind.
Finally, I shall look at the role of these characters. The relationship between the modern allies of the Luminary and the four heroes of legend focuses on the roles that each person serves. The Luminary is treated as the reincarnation of Erdwin, his predecessor. Serena and Veronica are explicitly treated as the reincarnation of the sage Serenica, dividing her characteristics and powers between themselves. 'Eight' is an explicit successor to Drustan, having been born of the kingdom that he founded, and following in his footsteps as a powerful warrior (following the trial at the Kingsbarrow, I believe that Sylvando also embodies Drustan to an extent, reinventing the role with characteristic flair). As a powerful sorcerer who would later master the arts of Angri-La, as well as the spells that Morcant himself wrote and left in Sniflheim's library, Rab is the most overt candidate to fill the sorcerer's role in the modern age. However, much like Serenica and Drustan, I believe that Morcant's role is divided in the modern day between two people. Erik retains some of Morcant's physical qualities, and also fills his most important role.
Erik was the Luminary's first, and most stalwart, companion. They spent the majority of the game together, beginning with the escape from Heliodor. I believe that the Seer instructed Erik to find the Red Orb, and follow the Luminary, in order to fulfil the role that he ultimately failed; to aid the Luminary in defeating the Dark One.
Of course, these links may not necessarily be the strongest; a decent portion of this theory is based in speculation, though I'd like think that these small connections were an intentional way of deconstructing and reinventing the original four within the player's team. Please let me know what you think of these ideas, anything you might want to add, or theories of your own!