OK, I think i understand now.
You have a looooooooot of work to do and you need to be fluent in php, html, css and js . These are general steps , doing this in detail will take a lot of time.
first of look into single-estate_property.php around line 325 and see how the list of features and amenities is read.
then in adv-search1.php – put the code that reads the features and add the checkboxes
i suggest that all those checkbox inputs to be sent as array to advanced-search-results.php
then in advanced-search-results.php you need to construct a query that will filter the listings according to your search input data.
If you want the same behaviour on the map – you need to add those ammenities in a transporting array to js. This is done in function listing_pins() in pin-management
The you need to read the click events on the new checkboxes and in the google js files to set visible/invisible the pins