Lithuania Noble Sons ?

[Slaya]

why are these guys recrutable in citadel ? why not sooner ?!

[Vissewalde rex de Gerzika]

I dont know, but you have plenty of other cav available to you, so it should be ok untill you get to them, also you should consider using "add_population" to get your own citadels, because it is almost impossible(you need 10 chiv and all sualour decreasing traits/ancillaries) to do so because of the extra squalor that the human nation gets.