Customization of Wordpress site - open to bidding

Website is based on Listify wordpress theme and WP Job Manager plugin (with add ons). It is a music group directory where members (the artists) can create their own profile (choose categories, regions, load photos, mp3 files, etc.). 1. When selecting a Main Region on listing submission/edit form, all its subregions (which are hidden) must be automatically selected. When deselecting a Main Region, all its subregions must be automatically deselected. For example, when selecting "Abruzzo", also its subregions Chieti, L'Aquila, Pescara and Teramo must be automatically selected. When deselecting "Abruzzo", also its subregions Chieti, L'Aquila, Pescara and Teramo must be automatically deselected. 2. Mp3 player on single listing is not working on some smartphones, i.e. audio can't be heard. I need the mp3 player to work on all platforms and browsers. 3. On single listing "Add to Favourites" and "Get Free Quote" buttons on cover image need simple css adjustments as they don't display neatly on Chrome and some smartphones (like iPhone 6s). Buttons need to display the same way across all browsers and platforms. 4. On single listing, review average rating shows zero. It should display the actual average rating for each individual review. Changes need also to be applied to the Italian version of the website (sites are pretty much identical). Websites are both live, so we have to agree on a staging environment for testing purposes.