Oh, I love designing relatives, especially siblings! As for whether they look similar to or different from one another, it really depends on a lot of things.
For example, these two have a lot of similar features. Downturned eyes, darker hair, similar shaped noses, and similar skin tones.
And then here's their parents. You can see that they got their dad's nose, their mom's hair color, a mix of their skin tones, similar hair styles, and one's got his mom's teeth while the other has her eyelashes.
Then there's these two brothers, who look a little more different. Similar skin and eye colors and thick eyebrows, but not much more than that. They take traits after each of their parents. Dude on the right looks a lot like his dad minus the hair color. Guy on the right takes more after his mom.
These two have roughly the same amount of differences, again, taking traits from different parents but sharing some others.
Finally, these two, who have so many differences that characters in-universe often don't realize they're brothers. This is because they take strongly after each of their dads.
This made designing their mom a little difficult, but I settled on some traits she could give each of them.
I have more characters with relationships other than two brothers, but I wanted to focus on my main characters now, plus, some of the other relatives are spoilers right now.
