Small corrections on a online store with Custom CMS - Front and Back -- 2

Live site, done with our custom CMS on PHP, Javascript, MySQL. Will share all code on bitbucket. We have some corrections to do: 1. Changes on quantity calculation: There are products that are sold in packs (e.g. 6, 12, 18, etc.). The interfaces where the quantity of the Product can be chosen (Product and Shopping Cart details) should be changed so that: a) When the customer selects a quantity greater than a multiple value of the pack, that quantity must be updated at the same time to the multiple value greater than the pack quantity. b) When the customer selects a quantity below the minimum pack quantity, the system must allow this value and no changes are required. E.g.: Considering a product with pack quantity 6. If the customer enters the value 5, the unit value for 5 items will be calculated normally. If the customer enters the value of 7, the system must update this quantity to 12. If the customer enters the value of 15, the system must update that quantity to 18. And so on. 2. Changes in product import functionality Ensure that the Product Import feature is correctly importing the value from the "Pack Revendedor" field to the "Pack Revendedor" field in the CMS. 3. Front-end ajust for Firefox Correct the display of the Product Quantity field (front-end - product detail interface) when displayed in Firefox, because in this browser it is displaying Up and Down buttons, even allowing the selection of a negative value. In other browsers is displaying correctly. 4. Back-end and Front-end ajust Change in back-end and front-end the Delivery Rate calculation, to consider different sizes for different customer access profiles. The site is in Portuguese. We expect the work to be done within 8 hours.