Everyone keeps saying they dont look alike but her eyes look very similar to the Duke's?

Yes, because for some reason they only believe that a daughter would only look like her mother?

The maid is the one that since the start believe that she's the real daughter.

Assuming the population is like real life, brown hair and eyes would be extremely common too and darker colours are typically dominant genes. If one or both parents have relatives with the gene, it makes perfect sense for Lilian to have them. Its actually weirder to just make a perfect combo like Swan. The logic of everyone in the story but Mary and (I think) the butler is annoying me sm