you won't be able to build the nightblade without using elf unless you want to allow humans to be able to take "elf points"
Here's the tl;dr:
every human class is made with 4 points and gets to go up to level 14. points get put in things like "fighting", "hit dice", "thief skills", "dive magic" and "arcane magic".
Fighter is fighting 2, hit dice 2.
Cleric is fighting 1, hit dice 1, divine magic 2
Thief is fighting 1, Thief skills 3
Mage is arcane magic 4
Other human classes are variants on this, as well as some extra magic.
Ok, then there's demihumans and all the other non-human classes. right off the bat, their maximum level is 13. So even though the Dwarven Vaultguard is Fighting 2, Hit Dice 2, Dwarf 0 - essentially the same as a fighter, he caps at 13th level.
the non-human races can take up to 4 points in their race value, and that does something different for each race. Every time they do this, their max level goes down by 1 (in addition to XP cost changes). In the case of elves, points of elf stack with points of arcane magic. this is how the elven spellsword can be a full mage but also nearly as effective as a fighter in combat.
Elven Spellsword is Fighting 2, Hit Dice 1, Arcane Magic 1 (a total of 4) plus Elf 3 (reducing their max level by 3 to 10).
Elven Nightblade is Fighting 1, Hit Dice 1, Thief Skills 2 (a total of 4) plus Elf 2 (reducing their max level by 2 to 11).
There's no way to give a human class, with just 4 points, the same amount of fighting skill, hit dice, thief skills, and arcane magic as a nightblade by default. I would say the simplest thing, if you're dedicated to the idea, is to use Zaharans in your campaign and say they're just a more magical kind of human. Zaharans have slightly different racial benefits from elves, but like elves, extra points in Zaharan raises their skill in arcane magic. In this way, you could duplicate any class you wanted that was an elf with a "human" and it would still be balanced.