Fixing a bug on a legenda theme wordpress site

I am currently facing below issues on the site [login to view URL] Below are the issues • Latest added products added is not on top of the collection list? (Problem solved only on collection page when first launched. After sorting doesn’t work anymore.) • Upon selecting of Brand, auto-sorting of sold items to bottom is not working. Same for both desktop and mobile platform. (Problem not solved) • Upon selecting of Brand, e.g. Audemars Piguet. There is duplicates of same product shown on the list. Same for both desktop and mobile platform. (Problem not solved) • After selecting of Brand, when selecting back to any, watches are sorted according to branding from A to Z instead of original page of latest products at the top of the page. (Same when selecting on location and happens on mobile platform as well) (Problem not solved. Now not sorted according to branding from A to Z and not according to original page of latest products at the top of the page as well.) • After selecting of Brand, click in to product to view and click back button on browser, sorting function fails. Watches are sorted according to branding from A to Z instead of original page of latest products at the top of the page. Clicking on the same brand as selected earlier fails to load selected brands again. Same for desktop and mobile platform. (Problem not solved.) The theme has been previously heavily modified and my previous developer abandoned the project. Please read thru the requirements!