I will give you root phpmyadmin and sftp access
then i will tell you what to do
1. modify some post meta whenever specific post type(ad_listing) was modified
2. add upload file function in front end when user add post_type(ad_listing) (if possible, i like front end similar to wpforms)
then you fix it and send me the new files (with a list showing me which file is modified)
It’s preferred to fix this creating a new plugin or using childvantage theme.
If it’s not possible, then change core theme
the site was using apptheme classipress 4.2.5; if you have ever worked with apptheme or better even apptheme's classipress; you will be strongly preferred.