If the star is needed to "reach" the subsequent nodes, yes, you must keep at least the minimum points in it to keep the subsequent ones unlocked.

Removing your CP from the preceding node will remove it from all subsequent ones.

Frogmother wrote: »

Is "Weapon Expert" needed to get the bonus from the other stars in the cluster?

E.g.
I skill weapon expert to unlock the other stars and skill them. Then I remove all points from weapon expert (the other stars keep their points). Will I still get the bonus from them ? e.g. from piercing?

In this case, Weapon Expert is not needed to unlock the other stars. Piercing is the one that unlocks the rest. As tmbrinks said, if you needed to put points in to unlock other nodes, then those nodes get refunded and locked when you withdraw the points from the controlling node. Since you can withdraw points from Weapon Expert without losing Piercing and the rest, you can see that Weapon Expert doesn’t control access to them at all. But if you go below 10 points in Piercing, then you will see anything you invested in Flawless Ritual, War Mage, Battle Mastery, or Mighty will be removed automatically and those nodes inaccessible until you reach 10 in Piercing again. That is the starting node.