User blog comment:Percy Jackson12/The Seven/@comment-86.164.6.183-20111016212856/@comment-3146930-20111016214954

They are set in the same universe, but they care kept apart for obvious reasons with only a few passing mentions to each other. Also, if Nico joined that would mean two children of Hades. Lastly, we know the last member is a child of Athena/Minerva so it isnt someone from the Kane books