Please follow this link.
When booking space for your Groupon, select the number of Groupon guests that will be coming. Do not select other ticket types as they will create a new charge. This will hold their spots and not prompt for payment as you have already done so via Groupon. Example before for a 2 Adult and 2 child Groupon.
On arrival you will be asked for Aquatarium receipt/ticket as well as your Groupon Coupon.