I wouldn't be opposed to the twins being members of the League. Maybe have Hawkman and Green Arrow as reserves. I feel like we need a GL, maybe with John Stewart since Tony fills the Hal role pretty well. But ultimately, as long we have a core seven, I think we'll be good. So maybe...
The Justice League of America
Superman - Leader, founder. The face of the League.
Batman - Financial backer, founder. Owner of the Hall of Justice.
Wonder Woman - Themiscirian ambassador, founder.
Iron Man - Secondary financial backer, primary tech supplier, owner of the Watchtower.
Scarlet Witch - Wielder of chaos magic, potentially the team's most powerful.
Quicksilver - Resident speedster, secondary mutant representative.
Martian Manhunter - Mars' sole survivor, founder, the League's SHIELD representative as "Agent Jones".
Reserves
Captain Marvel/Carol Danvers - Test pilot and Agent of SWORD.
Green Lantern/John Stewart- Lantern of Sector 2814, successor to founder Hal Jordan.
Aquaman/Arthur Curry - King of Atlantis, founder.
Hawkman/Carter Hall - Thanagarian recruit, reincarnation of Justice Society founder.
Green Arrow/Oliver Queen - Star City vigilante, The League's PR rep.
Black Canary/Dinah Lance - Daughter of JSA founder, original founder of the League.