You can display cameras using Alexa verbal commands on your Fire TV from Nest, Ring, Blink, and many others as a SINGLE camera. Currently there is no way to display MULTIPLE cameras at the same time.
TinyCam is an Amazon Apps Store app that can display multiple cameras at the same time on your Fire TV. The TinyCam Pro app is available in the Amazon App Store for Fire TV and Fire Tablets. The free version is available only for Fire Tablets. The easiest way to install the app is to use your computer to order it and “deliver” it to your Fire TV or Fire Tablet.
Once installed and configured, you can display your multiple camera setup by saying “Alexa, launch Tiny Cam”
Although the app is capable of supporting many different brands of cameras, I am only using it with Nest and Wyze. There is no support for Ring or Blink and the Nest support is only 1 frame per second, usable but very slow