Circe is describing to Odysseus the second way to his homeland. The first she described at 59. Here is the context and the structure of the antithesis marked by the correlation μέν...δέ:73. οἱ δὲ δύω σκόπελοι ὁ μὲν οὐρανὸν εὐρὺν ἱκάνει
Two things I don't understand:56. ἔνθα τοι οὐκέτ᾽ ἔπειτα διηνεκέως ἀγορεύσω,
57. ὁπποτέρη δή τοι ὁδὸς ἔσσεται, ἀλλὰ καὶ αὐτὸς
58. θυμῷ βουλεύειν: ἐρέω δέ τοι ἀμφοτέρωθεν.
59. ἔνθεν μὲν γὰρ πέτραι ἐπηρεφέες, προτὶ δ᾽ αὐτὰς
...
73. οἱ δὲ δύω σκόπελοι ὁ μὲν οὐρανὸν εὐρὺν ἱκάνει
1. What is οἱ standing for?
2. Is it εἰσι understood in each element of the antithesis?
I would expect something like this: ἔνθεν μὲν γὰρ πέτραι... ἑτέρωθι δύω σκόπελοι (εἰσι): "...there are rocks... there instead are two crags". What confusses me is that there is οἱ instead of the expected ἑτέρωθι.
a. If οἱ is a demonstrative pronoun, then why is it masculine and plural, where it's antecedent is femenine and singular (ὅδος)?
b. Could be οἱ the article of σκόπελοι? I thought that Homer always ommits the article in the nominative case, moreover I would say that δύω σκοπέλοι has more sense as an indefinite subject (the first element of the antithesis indeed is "πέτραι" and not "αἱ πέτραι").
c. Is it perhaps that οἱ has a deictic antecedent? So Circe points out with her finger the two crags and says: "οἱ δὲ δύω σκόπελοι...". I don't think so, but it was my last desperate try.