Mmmm. If only one of the LEDs works when connected to the Crumble (i.e. if you try to connect all of them as the first LED), then it sounds like the other WS2812Bs may be faulty. If you remove the wiring you’ve added and connect each one in turn, you could be fairly sure if the LEDs are good.
It’s also worth noting that the WS2812Bs no longer seem to have reverse polarity protection (they’ll pop if the polarity is reversed). The Sparkles have an additional protection diode to prevent this.
Hope this helps,