I think they are possibly the arrow triplets instead of twins? Misterious-shadow girl’s silhouette looks a lot like crow and raven’s to me.
okay so at first when i heard that Odin has three sisters i thought they might be triplets but the fact that they refer to themselves specifically as twins made me question that idea and think that the third sister was probably another age entirely
HOWEVER i just remembered that it is impossible to have identical triplets (because it is impossible for an egg to divide into three) but when a person has triplets it’s possible for two of them to be “twins” so to speak
when you have fraternal twins the two eggs are separate with totally different dna but if one of them divides then you have two individuals with identical dna and a third individual who’s dna is different but the three are still triplets
so maybe when Raven said “he thinks i’m dumber than my own twin sister” she simply meant “we have the same dna but he still thinks i’m stupider”
maybe sister number three IS their triplet