The other 6 could be the nobodies of Dilan, Luxord, Axel, Demyx, and so forth. Eventually we didn't know Saix was there because he looked indentical to the other Xeohanorts and we couldn't tell by the physhique of who was who. But when he went after Lea we saw a weapon in his hand and his face. Xenmas stated that they have two hearts or could so maybe he made those nobodies hearts out of the organization members that were defeated in KH 2. He already can use Xaldin, Saix, Axel, Demyx, Luxord, power weapon in that game and it would explain how he can still use them.
This would explain why he didn't seem that much worried about Lea interfering. Xeohanort didn't as much either. Briag though seem disturbed. Lea also got in the way of the power to save Sora by Xeohanort. This must mean something. Perhaps got affected.
Nobodies have the ablities to create clones so perhaps they can make manifestations of themselves and others as well. YMX, Xenmas, and Briag seem to make illusions or create dreams. So they could create more members with the ones that were killed off.
Xeohanort army we do know.
Xeohanort
Xenmas
Xeohanort SOD
Young Xeohanart
Xigbar
Saix
This one makes more sense with the others
Xaldin
Luxord
Axel
Demyx
Ventus
Terra Xeohanort
Can' think of other one except Replku or even Vexen. For all we know he never woke up or was still unstable.
One of the Xeohanorts mentions Xeohanorts of the past and the other organization members are from the past.
Luxord, Demyx and Axel have control over their own lesser nobodies as well besides Saix and Xaldin and Xenmas. Roxas did as well, but he is a different story. They were good manipulators and deceitful.
Another possiblity
Xaldin
Luxord
Demyx
Axel
Marluxia
Larxene
Then again Saix knew that Marluxia, and Larxene were traitors in CO so I doubt it would be them. They wouldnt want to come back to the organization, but I am not counting them out. Larxene didn't want a heart, Marluxia I think didn't either. They wanted their freedom, but also power.
Yes I know that Axel and Lea are different, but it still points to that Axel is still around somewhere. Nobodies having two hearts is another example of it. Plus we don't know if Lea had powers before his nobody Axel came into the picture. We do know that Lea kept his powers when he woke up. Axel also knows how to kill and is manipulative and deceiful as well. If you reborn a nobody without any connections to certain people then you have Axel from COM.
Saix could bait Lea since Roxas isn't in the picture anymore and plus Lea would want to save Isa. It never explained Axel's pain so this could be it to save Saix/Isa. Also wasn't Lea going to find the other members?
Demyx was the only nobody who worried that Axel was missing from the organization and never pried him as a traitor like ther others. He could be a lost sheep in so many ways. He hates fighting, but he does know how to if he is forced. He also hates Saix, but never Axel who is in fact fire while Demyx is water. I can see him interacting with Axel/Lea and also Axel defended him in Days so that must mean they have history together. When Axel was Lea he mentions he had friends not friend. So Isa wasn't his only friend. Perhaps Xigbar kept them apart. Axel and Demyx could be rivals really easily.
Luxord is loyal to the organization so I am sure he will be back. He also has this time warp thing as well. Not to mention Normua's favorite organization member.
It is more logical with these characters since it would be stupid for Noruma to create more new characters when you have others that were already in the mix.