Ducks do not need constant access but a couple times a week AT LEAST!!! Your ducks and chickens could give each other diseases in some situations, you could try to keep them together, lots of people do! Some people have separate runs and houses because ducks are VERY messy. And they throw their...
The more experienced hatchets may be on here soon if you need help with that! This link will tell you most of the basics!
https://www.backyardchickens.com/t/750869/raising-and-caring-for-ducklings#post_10611711