You have to find a new owner, plain and simple. Even if they were the wild type of duck, they are too tame and dependent on people to release in the park, not to mention it's cruel. Try asking your teachers or other adult relatives. I don't know if you live in a city or in the country, but perhaps you can find a farmer to take them. Are they male or female?
Be aware that some people may want to buy your ducks for food. So, if you don't want that to happen, you have to screen your buyers.
Be aware that some people may want to buy your ducks for food. So, if you don't want that to happen, you have to screen your buyers.