Young twenty-something and late twenty-something guys says to me "an attempt to recreate the dynamic between Luke and Han," but who knows? I could totally see a Luke/Biggs dynamic playing out between the two late-teens female characters (again, this is going off of nothing but an ultra-vague casting call).
Still plenty of unknown factors, though.
Lucasfilm confirmed it's real, but maybe only some (or none) of these roles are main characters.