Hi and welcome to BYC - thanks for joining us. I have never kept ducks, so I can't help you, but if you could post on the duck forum - https://www.backyardchickens.com/f/42/ducks as most of the peeps there have, or do keep chickens and ducks.
Are you asking about for just when they're chicks and ducklings, or that and when they're grown? Yes, they can live together, but there are some things you'll need to keep a close eye on.
• Make sure everyone is getting along well. If there is any "bickering" among them, I would separate them.
• Ducklings love water. It's a well known fact that ducks swim. When they're little, they will make THE BIGGEST mess in the brooder with the water dish. You'll have to change out the shavings (or whatever you use in the brooder) daily. And when they're grown, they'll make even bigger messes.
I wouldn't keep bantams with them, because they can easily drown (if you have a water bowl for the ducklings? or be trampled on under those big webbed feet.
. Lots of people combine ducks and chickens, and most people have good results. Definitely check out the link provided by @redsoxs.
I wouldn't keep them together. ducks love to make a mess with water. Chicks do not like getting wet and since their feathers are not water repellant, they can end up chilled - not a good thing.
I would strongly recommend against it. Ducklings make a horribly mess of their water and if you don't clean the brooder at least once a day, you'll end up with sickly chicks. Not to mention that ducks are big and rambunctious and banties are small and fragile.