Could you post some pictures so we can try and identify them?
Ducks need their water changed several times a day as they need to fully submerge their heads to clean their eyes.
Ideally, they will need a pond of some sort, it could be a fish pond but larger, and that should be changed every few days.
If you have females, you will need to provide crushed oyster shells so they can form their eggs.
We need to find out what gender they are - you can keep same sex groups together but you shouldn;t have one of each as in the breeding season, the female will be over-mated and will be attacked - you can keep one male to three females.
You can offer them treats such as sweetcorn, chopped cucumber, lettuce, chopped tomoatoes, peas etc.
When they start molting, provide them with chopped boiled eggs as extra protein so they can get over it quickly.
I hope this helps! Feel free to ask me questions!