Wordpress Website Changes - Plugins & Theme Edits

We have a Wordpress WooCommerce website: We need for 4 following issues resolved. Website Changes: 1. Coupon redeem page Currently the coupon redeem page is not working. This was previously coded by another freelancer – we need this debugged and future proofed. The page should auto-recognise coupons, redirect customer to checkout, add the correct item to the basket and apply the coupon discount. 2. Checkout page We have an age verification box at checkout that requires people to enter a date of birth. We’d like this plugin fixed. It currently is in the wrong format – MM-DD-YYYY, Needs to be DD-MM-YYYY – There is also has a Japanese logo on the dropdown datepicker, we need to remove this. (We’d also accept an alternative plugin or custom coded solution). All it needs 3. Age Gateway – Mobile number keyboard On age gateway – make keyboard numbers show up for mobile users (if possible) 4. Theme Edits for mobile On one of our pages, we would like the some of the box elements to become 100% width when viewed on mobile. Currently they are three side by side boxes, that move responsively with gaps, but we need them to become full width on mobile/narrow width. All changes made should be saved in our child theme in a way that is future proofed against updating of plugins or themes. We are happy to provide further details upon request. We will ask you to confirm you are capable of completing all tasks before we offer you the job.