Add functionalities to custom shopping cart

My website is [login to view URL] and it has a custom admin panel/database coded with Codeigniter/MySQL. The website sells tours using a shopping cart system. Please check how the site is working before you bid. I need to add the following functionalities to the system: 1) Shopping cart page: Have link near dates at shopping cart page, to popup same calendar datepicker as tour page and allow date change. Note: datepicker functions already implemented, you only have to put the links and copy functionality to cart page. [login to view URL] 2) Shopping cart page: When user clicks checkout button, system checks if 2 or more tours are selected for same date and sends message to change the dates. [login to view URL] 3) Tour page: group size and date default values are pre-selectd based on last item added to cart [login to view URL] 4) Tour list page: checkmark near tours that have been added already to cart [login to view URL]