whats the best way to run 2 sites but use same database with same prefix on Drupal 7? basically i want to create a duplicate of the site and place it in a separate folder to the main site on the same domain, and have both sites use the same database, so that if one site changes something it changes on the other site too

basically im gonna be developing on one version of the site, while a designer works on the design and CSS on the other site, but he may also want to edit menu links, blocks etc so he will need to be able to write to the database as admin, once both dev and styling are complete we would copy the theme folder from the designers site in to the dev site and delete the other site and use just one for launch

what would be the best way to do this?
It is quite possible in Drupal. Make sure settings.php on both the instances are identical (I assume both the instances are hosted on a single server).

However, better way to manage such a scenario is to use version control.