Combining elements from 2 themes

I have a client request to build a website using the following theme:

https://theme10.themeszen.com/

but to include the portfolio functionality from this theme:

https://theme14.themeszen.com/

the way it sorts categories and moves them around etc.

I am fairly comfortable working with and editing WP files, but I am not sure where to begin with trying to bring that portfolio functionality into the first theme. How do I go about doing this?

Thanks!