The Witch King's death

[Carannillion]

Sauron did infuse the One Ring with a part of his own spirit - or used a portion of his power in its creation - so that it would have been very draining for him to create even more.

As for the rings of the Nazgûl, I tihnk that whether Sauron kept them, or the Nazgûl were wearing them, they would still only work for one person at a time, like the One. Even though former ringbearers were drawn to it, they couldn't control it. Sauron had some influence over it even when somebody else had it because the One Ring was a part of Sauron.