You need a courtyard made out of netherwart, and the blocks in the courtyard, and outside should be souls and, also you should have Martha castle out of netherbrick and netherrack, but nice build, I understand how hard it is to bold a large scale castle.
P.S : Y U NO build castle in nether!

Please post me if you want the Castle to be in different blocks! I will change them to whatever block you like :)