OK so if I am deciphering the clues for the 13th...
Matthew L. Martin wrote:
If the line and the Kargatane's participation had ended at Gaz XIII, it would also have brought some things full circle.

And
Matthew L. Martin wrote:
The full circle quote was a meta-comment in regard to the Thirteenth and the Kargatane design team, actually.
What I am taking this is that we should look for the first product that the Kargatane worked on. Unless I miss my guess, this is Carnival which Mangrum wrote. We should look for the 13th in this product.
Now lets look at another clue...
Matthew L. Martin wrote:
The last plans were for the Thirteenth Dukkar to be a character who has seen print . . . but whose abilities are generally latent and who is in a situation that would make it tricky for Azalin to get a hold of him.
In the Carnival it would be very tricky for Azalin to get a hold of him. (Also, Note that he says *him*. So the 13th is male.)
Matthew L. Martin wrote:
The Thirteenth Dukkar's mother has also received a writeup.
And
Matthew L. Martin wrote:
The mother of the Ultimate Dukkar has been guessed on this thread, but that of the Thirteenth has not.
Which all leads me to this (which appeared after the previous comment was made):
Drinnik Shoehorn wrote:Has anyone suggested that the Familiar from Carnival is the Gentleman Caller's child?
The Crimson Rose was pregnant when she arrived at the Carnival and the Skurra-vera prevents her and the Familiar from talking about either of their pasts.
So no one knows were he comes from or who his father is.
I think Shoehorn has nailed it. I believe that the Familiar is the 13th and is the son of the GC and Crimson Rose. This fits the bill absolutely perfectly for the 13th.
I have no idea on the Ultimate.