To allow buyers to purchase multiple items at once, typically you would use our Cart button codes (rather than Buy Now buttons), so buyers would simply click the Add to Cart button for each item they want to order.
Simply copy the Add to Cart button codes we provide for each product in your Seller Admin, and paste them into your page wherever you want each button to appear. You can put them all on the same page, or on separate pages, however you wish. Just make sure you also paste at least one complete block of your View Cart code (it's the same for all your products) on every page that has any number of Add to Cart buttons for specific products.