Why never once yana mention ciel's twin brother name ?

probely gonna say it in the Great final he probely gonna say it to Sabastion when you make deal with the devil or when we are back at the timeline we where

Actually Our Ciel's name isn't really Ciel.
Technically Ciel is the name of Real Ciel, the older twin cuz he's more recognized as Ciel Phantomhive. So we only need to know Our Ciel's true name and besides, Sebastian never calls Our Ciel as Ciel and since he only tells truth, I believe that Our Ciel's name isn't Ciel. This is very irritating actually ╥﹏╥. Yana-san should just give Our Ciel a name.