Lightbringer (better known as Illumina in FFVI) can only be equipped on a Red Wizard, which I recommend you do. Give the Knight Ragnarok or Ultima Weapon at your discretion. If your Master has high HP, Ultima Weapon might be good for him (so the Knight can use the Knight-only Ragnarok). Judgement Staff is good for a Black Wizard, although I would also consider Masamune if the Intelligence bonus and Flare aren't important to you.