Pekin looks likely to me!
Ducklings have somewhat different water needs than chicks, and need three times the niacin. They grow amazingly quickly, so watch to make sure that in a week the ducklings are still okay in with chicks. It may work out, but just keep an eye on them.
Ducklings can drink from chick waterers at first - that is what I used. But they need to be able to wash their entire heads to avoid foamy eye and sinus, eye and ear infections, so think about how you can do that without creating a drowning hazard for the chicks.
They like to play in water, too, so they can dampen a brooder if you don't have the waterer set up to minimize splash and spill. They cannot help it, they are just duckies
But they are so sweet!
See if a search of the forum on duckling brooder, duckling water gives you more ideas.