who are the two vices speaking in part VI of the rime of the ancient mariner

We aren't told WHO they are, it's just a different form of narration;

"In Part 6, the two voices offer a narrative and stylistic break in the poem. Whereas before the text was unbroken, their speech is structured much as in the script of a play. The voices are also omniscient in that they know everything that has happened up until now, and are able to offer the Ancient Mariner a more complete explanation of his situation. The manner in which the voices are presented lends a didactic, narratorial feel to their words. The voices leave because, like the Wedding Guest, they have somewhere to be; the second voice urges the first: "Fly, brother, fly! More high, more high! / Or we shall be belated." Yet unlike the Wedding Guest, the voices are not riveted by the Ancient Mariner's tale and can continue on to their destination after briefly stopping to consider him. They are like the two other guests walking with the Wedding Guest when the Ancient Mariner stops him; while his tale may interest them, they are not compelled to hear it."