In Turn Coat Ebenezar sais that they are "Some wizards. Some key allies." Now Vadderung definitively fits the key ally box. But he uses plural, so there is at least one more. We also know from Changes that they all have wizard staves. There is only one that we have seen that can be considered a key ally and that has a staff, and that is Eldest Gruff.

On the wizard side we have a clue to the identity of one of the wizards in the grey council. During the battle in changes, Harry hear someone yell "Fuego". Most of the older wizards don't verbal out their spells. We can then assume that this is one of the less experienced of the members of the grey council. Have we seen anyone that fits so far?

Otherwise Martha Liberty is one that seems to be a obvious choice. Chandler is a good possibility, but could be wrong as he is most often seen without a wizard staff.
Klaus the Toymaker was established as an ally of Ebenezar in Summer Knight and seems JB has thought of a lot of backstory for him. I peg him as a member too.

So 3 of 6 so far. Listen-to-Wind was out of commision. Luccio is possible, but we've never seen any indication that Ebenezer trusts her like that. Ancient Mai and Langtry are unlikely, they both seem to believe too much in the institution of the white council.

Rashid I think is more likely, since Ebenezar changed his mind about him after talking to Harry in Turn Coat.
I also like Montjoy for the Grey Council.

Now, i have no idea about the last one. Wild Bill and Carlos seem too inexperienced to be trusted fully. Also don't think Carlos uses a staff. I would peg Chandler over Luccio if I had to pick one of the previous of the unlikely choices.