Was reading it and thought they were siblings… I had to reread everything cause I was like no way they incest
Some noble families demanded specific features. A wife in this case though she might be intelligent and capable, her appearance should compliment her husbands making him look better by sight alone. Depending also may have them both appear like a force to be respected. Also the mixing of features for children as well. The family in the story are known for Golden hair so of course the heir would marry a woman who will produce golden haired children. We see those children from a far in an early chapter. Now i personally think that's partly going on in this comic but its also it might just be a coincidence.
I think it was mentioned briefly that they are distantly related probably extended cousins
The Duke's family branched off from imperial family, so they have similar features, in this generation the duke married the princess so they both look similar.
Why do the husband and wife look like twins?!