2 way mirroring of cells in google sheet

Hi im working on a portfolio and it has to be live. I actually manage to do it in excel via macros. But since we need to use the portfolio live so i have to shift over everything in Google sheet. However, i don't know how to read and code google app script and i don't know how to mirror cells that can be both updated and edited by the user in different sheets.

I hope you can help me on this.

Here's the link - https://docs.google.com/spreadsheets...it?usp=sharing