5 week ducklings won't help a broody chicken not be broody. 5 week ducklings are pretty big. And, with a silkie, she's just going to go back to being broody. Have you tried a broody breaker? I've heard Silkies are the worst and are constantly broody. So, even breaking this round, she most likely will just go broody again. You should probably post a separate question in the behaviors forum regarding your broody to get ideas of how to break her.
As for the duck question. So far I'm enjoying my runners. They are quite a bit of a nervous breed. If your yard is fenced, free ranging will definitely work. They are great foragers. But, I would still contain them in a run of sorts so they can get to know you and learn a routine.
I'm not sure what you consider noisy. Some things that I have read said they are quieter than other breeds. They make quite a bit of noise in the morning when they want fed - on par with my chickens. If you want a cuddle duck, then runners most likely aren't the choice. Of the mallard derived breeds, females quack loudly and the males are considered quieter.
Also, I've got muscovy they are definitely quiet compared to runners. The runners will make a mess - that part I know to be true. If silkies need a dry environment (as all chickens do), ducks in general aren't a good choice. I've got separate areas for my ducks and chickens. But, due to the runners being new, they are in with the chickens so they can be confined until they learn to stay in my yard (I have no fence). They have an area in the chicken run to make a splash and they do. They are fun to watch when they think I'm not watching.
You would need to tell us more about your set up so we can help gauge how much room you have to accept new birds.
