I say brood them separate. Ducklings are such messes. Damp can be deathly for baby chicks.
After they're coop age, we've combined ducks and chickens with minimal problems. Now, I have a large coop and run, so there's no space issues. Feed is in the coop, water is out in the run. So, I don't have Wet Coop Syndrome or anything like that.
We used to have a kiddie pool for the ducks. Had one for years and no problems.
I don't know what it was about the chicks this year, but they were dumb little things I guess. I lost I think 4 to drowning
. Put a ramp in there, etc. So, out went the kiddie pool. We're down to one hen duck now, and she does just fine with a large Little Giant gravity waterer. I guess the pan is deep enough she can do her thing. She does make the pan very dirty, though.
Our ducks usually prefer to sleep in the run. I have 24/7 access between the coop and run, they decide where to sleep.
Ducks overall are more aggressvie than chickens. Drakes can be quite aggressive to other birds, and can even drown hens when trying to mate. That's unusual, but it can happen. So can a drake damaging a chicken hen when trying to mate. None of my roosters have ever stood up to a drake. I have enough space the chickens can run away, and enough duck hens to satisfy the drake.
If you're tight for space, I'd reconsider keeping them together. A separate pen may be best.