In the very first episode of the Greed Island arc, Gon and Killua meet up with two of the Phantom Troupe members while in the auction.
The members say they will no longer hunt our heroes because... something to do with their leader's Nen surviving after death? I watched the episode again, but it doesn't make any sense.
Why is the Phantom Troupe no longer interested in revenge against Gon et al?
Kurapika placed his judgement chain on the Chrollo Lucifer, the Phantom Troupe's leader. The Phantom troupe knows that and that Lucifer is currently seeking the help of a Nen exorcist in order to remove it.
Now why did they let Gon and Kirua go? Well because they want nothing to do with Kurapika anymore! If the person who placed a Nen dies, his Nen becomes much stronger after death, and a much more powerful Nen exorcist would be required in order to remove it. Actually, only a handful of exorcists have the skill to remove the Nen left by a dead user [1]. Or, since Lucifer is at this point weak because deprived of his Nen, he might even die.
The Phantom Troupe knows this and therefore they do not want to have any more direct or indirect interactions with Kurapika. If they were to harm Gon and Killua, Kurapika would surely come seek vengeance once more. If they were to fight off Kurapika, they would have to hold back to make sure he survives the fight. That would be not be an easy feat as Kurapika is not so weak.
[1] Chapter 120, page 13 (not shown here for compactness)
Some of this is explained on page 12 of Chapter 120:
The Troupe can't touch the kids until the Judgment Chain is removed from Chrollo.
They are indebted to the kids somewhat for what they did for Pakunoda.
They like the kids in general. Mind you they did want to recruit them before all this started.
It's suggested that they they happened to like the duo and feel grateful for what they have done for Pakunoda.
However there's also an alternative way of looking at it:
Kuroro thinks Kurapica's weakness is his friends. However by that time he also knows their backgrounds. Freecs and Zaoldyeck.
To attack them while the Spiders are incomplete is counter intuitive.
They all know most of them will die, and to provoke a confrontation without their Leader is out of the question.
They will leverage Kurapica's weakness in the best time Kuroro thinks is possible. Also considering the implications of having killed 2 offsprings of arguably the most well known names in the world of HxH. Possibly forcing the prediction to come true.
Chrollo isn't as sentimental as the others when it comes to preserving their group.
