User blog comment:Bennlimos/Understanding the Zoldyck Family's Nen Situation/@comment-10528819-20151018141034

Let me try to fill the holels a litlle bit (I might, and most likely will, fail)

1. They probably didn't want him to learn nen yet. By the time Killua seemed coky and undisciplined and making him stronger would probably  just make the situation worse

2. Milluki probably know about nen but didn't knew you needed to use nen to get into Greed Island, even the Troupe that knew about the game and know about nen seemed to realize you would need hatsu to activate the game right away

3. This is probably the hardest one, and I don't have a good answer for it. However Killua without nen can walk in a way that seem he has multiplied and can turn his hands into claws, maybe he knew about Dragon Dive but though it was something like that

4. Kalluto probably learned nen way earlier than Killua, due to the fact that he's passive throuwards his family

5. When he left with his friends Silva probably decided he should learn nen by himself, and that sending someone after him would cause problems. Besides Killua probably would notice

6. Illumi put the needle on Killua's head for 2 reasons: 1- to protect him from stronger opponents (he not knowing nen, don't stop someone that hates him from knowing it)

2- to prevent him from turning over his family

7. Yeah, you explained that, don't sound like a plot hole to me

8. They knew about the needle because it from their interest that the needle was on Killua's head