Is there any way i could get youngest sibilings with me or i mean adopt them...?

im the oldest sibling out 5 kids... we where all in foster care houses so they splitted us up with some of my moms relatives so me and my sister and baby brothers went with my moms aunt and the other 3 went with my moms other aunt so my moms aunt the person we where with adopted us 4 but my moms other aunt hasnt adopted my other 3 sibilings and shes not planning to adopt them but now that im 18 i really want to have them come live with me would that be possible or not