Your concern about your auntie's fish eating your two goldfish are very legit.  For most goldfish , whatever will fit in their mouth they will consume, including other goldfishes.  Depending on where you live, if the temperature of the pond water (not just outside air temperature) is 50' F or below, dropping your goldfish from a warm environment into such cold water will be too much of a shock to their system.  They can survive in cold water, but only if the temperature decreases very slowly and they are allowed time to adjust.  Maybe you can hold on to them for a few more months until warmer weather arrives ( if you live in the usa), which should give you more time to decide whether or not the goldfish will be able to survive in your auntie's pond.