How to preview all local cameras available

Hi:
I am working in my own ui with the great jitsi lib api and I want to create a preview selector like in jitsi-meet with the preview of all local cameras available. ¿How can I get that and show to the user?
Another idea I have is to create a mix in my canvas of both camera, one big and one preview in the bottom left, how can I get the second camera to use in my render function of the effect?

thanks so much.