... No offense meant at all, but this isn't good. Get a heater, if you need to, make you dad drive you back to get one today, and return the boy. With two bettas in a 2.5 gallon tank, I'd be doing something like three 50% water changes and two 100% water changes a week at the least. Or, find good homes for all your goldfish that will properly care for them, and give one of your boys the goldfishes' tank. Be assertive. I'm assuming you are using your money, so you have a right to buy what is necessary to help your fish thrive... Not just survive.