is Yan Yi here the same rabbit from "Everlasting Love"?

yep!

The authors works are connected, i think desharow merman is connected here too

Desharow merman is not by the same author

It just has a mermaid theme but it doesn't have the same author as either one of the aforementioned, desharow merman is by 深海先生 meanwhile the two are from 麟潜 .

Ahh i see