The one on the right has their hands on their hips.
I think that member might be one who occasionally
has been seen in such a pose.
Xigbar comes to mind, but I think Demyx and Larxene
have also stood in such a pose as well.
Xigbar is known for spying though, so it
seems logical that he would be the one in
the background watching Axel and Roxas.
Plus Xigbar has been seen once before discussing
with Zexion about his observations, so it would fit
quite nicely if the two were Zexion and Xigbar.