In the purport of Srimad Bhagavad Gita verse No. 10.21,Srila Prabhupada says that

          "There are twelve Ādityas, of which Kṛṣṇa is the principal"

             So from the above statement of Srila Prabhupada we have come to know that in this Universe of four headed Brahma there are twelve "Adityas".

              The number of members in the category of "Adityas" is twelve and KRSNA is the principal among them. Our "SUN" is also known as "Aditya",so he is one of the twelve members in the family of "Adityas" category.

               So we have seen the examples of two members from the category of "Adityas" named as KRSNA and SUN (SURYA-DEVA) are both illuminating the objects of this Universe and now see another verse from Srimad Bhagavad Gita

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BG  15.12

yad āditya-gataḿ tejo

jagad bhāsayate 'khilam

yac candramasi yac cāgnau

tat tejo viddhi māmakam

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           In the above verse of Srimad Bhagavad Gita by the word “āditya” it can refer the “SUN” or the category of twelve “Adityas” as they also illuminate the entire Universe and VISNU (the Principal Aditya) illuminates the uncountable numbers of material Universes through His energies and that’s why Srimad Bhagavad Gita uses this line “jagad bhāsayate 'khilam” , “Jadad” means Universe,"bhasavate" means “is illuminated” and “akhilam” means every, so the total meaning comes in the form that “The light or ray energies of Adityas which is given by KRSNA illuminates every Universe(i.e uncountable numbers of Universes) of this material creation”.

              But if we use the meaning that “āditya” as SUN then the meaning become partial and we know that in the sayings of KRSNA there is no guilty or no mistake or no partialness like other beings of this material creation.

                    So please discuss about the responsibilities, activities and features of these “Adityas” (i.e twelve “Adityas”) in this Universe of four-headed Brahma.