how am i able to recruit special soldiers like Lannister Infantry or Stark Soldiers. I want to get these guys but idk how to become lord of Casterly Rock or Winterfell of that sort.
You, uhh, just answered your own question. You have to be lord of their castle. Karhold for Karstark, Twins for Frey, etc.
And to get those... You either have to be lucky, so king awards it to you, or you can take it by force.
Alternatively, you can recruit those from prisoners.