Well you have one blue, two blacks and one chocolate.
Their body shape is correct for a Swedish. I was expecting a duck that looked more obviously crossbred but your chocolate bird does look very Swedish.
The only thing that might indicate cross-breeding to me is on the black ducks. It may be the lighting, but it looks as if they have a mallard-type pattern on their faces. That would mean they are not pure.
Whatever they are, I hope you enjoy them.
To tell male from female, pick them up one by one. Ducks that quack loudly are female. The male will make a quiet, raspy hiss-like sound.
they definitely have a slight marking on their face. However, several of the pictures of "black swedish duck" on google have that as well. What do you think?
I don't know. They may be mostly Swedish with grandparents or great-grandparents of another breed, or it may be something recessive that pops up rarely (like the chocolate color).
I like the look of the black duck in back. I think that is the male. In the Swedish breed, males (ideally) have those big, "poofy" heads.
Earlier this year, I hatched out two clutches of Swedish/Pekin cross ducklings. Most came out marked almost exactly like a Swedish, but the black ones have some faint mallard-like markings on their faces, like yours. To my uneducated eye, these ducks seem to have a body type like the Swedish, but slightly larger than their Swedish mothers. The black offspring also have faint markings on their wings, like just a bit of frosting around the edges of some feathers, which I think I see on the wing of the duck in the foreground in your most recent photo. I have not noticed anything like this on the blue babies that hatched. I'm guessing your ducks are not pure Swedish.
Also, do you know how old these ducks are? They look a little raggedy to me, like my year-old ducks did just before their molt. My blue female's feathers became very rusty looking just before her molt - I remember thinking she looked like a chocolate. Her feathers were in poor condition, and looked very much like your "chocolate" does in the photo. She has since re-grown her feathers and is her original steel blue with no hint of the chocolate color. If your ducks are old enough to molt this year, I wonder if the chocolate color might not be permanent.
* Editing to add a photo. This is one of the ducklings from the first hatch, from my Pekin drake and a black Swedish duck. The mallard-type markings on his face are obvious. You can see the frosting on his wing as well. Both the brown face markings and the frosting on the wings appeared only in the black offspring (and appeared in all of the black offspring) - the blue offspring do not show these markings. All of the ducklings (black and blue) from this cross do have exaggerated white wing tips, which you can also see a bit of in this photo. I have attributed this to the Pekin parentage (in case you're not familiar with the breed, Pekins are pure white), and assume that it wouldn't appear in crosses with other breeds, but I don't know.