With the ducks in question being a year old already, the male may be mean to the new chicks. Or they may be afraid of the chickens. It's hard to tell. When they can live together is based on age and size. I had great success temporarily housing 5 3 week old ducklings with 3 6 month old pullets. The chickens weren't old enough to have any serious dominance issues (not like older hens) and the ducks were too little to chase the chickens off.
The chicks need to be at least 6 months old for size. The ducks, you may want to wait and find younger ones, or house these two separate and give them a dog house and a run of their own. Then let them meet during free range time and see how it goes.
A boy duck will try to mount other things once his hormones start going. Or he might not. But the hens need to be substantial in size or kept separate if the male duck is less than ideal in his behavior.
The other thing to consider, is that ducks play in their water ALL the time. They can empty a 1 gallon waterer in no time. So you need to make allowances to keep everyone in clean water. It's not too big a deal when the ducklings play in their own dirty water. But the chickens can't be drinking it like they do. I set up a waterer for the chickens out of the ducks reach on a platform. The water the ducks throw around can easily soak through the bedding if you don't have it set into something.
Or you need to arrange one of the hanging waterers, or auto water supply. Something. The way ducks live versus how chickens live, they're not ideal roommates. But it can work with proper management and planning.
