i am getting citizenship next year after i want to file for my parents but my Niece and Nephue also lives with them (my parents are legal gardian of them). becasue my sister in law is no more and my brother also not living with them (he is working out of state. so they living with my parent is there any way on that legal gardianship i can bring them with my parents?

There is no immigrant visa classification for you to petition for your nephew or niece even if there is a guardianship in place.

Please consult with an experienced immigration attorney with details on the case. Good luck!