On the Topic of the Blind Prophet...

As a member of the discussion group who formulated this question, the answer was not immediately obvious to me. The seer was an individual who gave advice to Creon, but there wasn't a singular individual who Karamat listened to above others; people who Karamat listened to included his personal assistant and his head of security.

That being said, after thinking about the role of the seer a bit more, it became incredibly obvious that the parallel to the seer was Karamat's wife. Circling back, the role of the seer within the story was to incite change within Creon to rescind his decision to prevent Polyneices' burial. In the case of Home Fire, the individual responsible for changing Karamat's mind about Parvaiz's burial was undoubtedly his wife; in class, it was mentioned that both achieved this means through threatening Creon and Karamat respectively. While this is true, the seer's threat was the only reason that Creon revoked his stubborn law, whereas Karamat's wife used a political threat as a pretense to get Karamat to come and speak with her as a father and husband rather than as a political façade.

The most clear parallel, and one I hadn't noticed for a while, was the names of the two characters: the seer is named Tiresias, and Karamat's wife is named Terry. As is clear, Shamsie didn't shy away from making one-to-one adoptions of Antigone's names and modernizing them to make the names of her own characters, and so Terry being a modernization of Tiresias is more apt than any other character in the novel.