I don't know about where you come from, but where I am, that's no longer considered normal to fancy yer cousin.Wait. If Ezra and Zeb are the brothers, Hera is the mom, Kanan is the relaxed dad that gets stern when he needs to, and Chopper is the generic grumpy uncle/cousin no one likes... What's Sabine?
I wouldn't call Kainen the "relaxed dad", just one that is a little less focused on the fatherhood side of things. And I'd say Chopper is more the younger brother, but a nephew or niece works too. Given Ezra clearly fancies Sabine, that obviously hamstrings a brother / sister dynamic between the two of them so I'd more put her as an older cousin to him.
I don't particularly like being mocked. Historically it has not been uncommon at all for cousin's to marry and no-one batted an eyelid when Charles Darwin or Albert Einstein married their cousins. And it is still perfectly legal through pretty much the whole of the Western with the exception of the United States. And it's not only legal but also pretty common through much of the Middle East and Asia. The reason it's illegal in most of the USA is because the USA had a big eugenics movement and there were popular fears about racial degeneration. (True). USA is not the whole world. In fact, due to something called the Founder's Effect a certain degree of cousin inter-marriage helps establish beneficial mutations in a population (look it up if in doubt).
Bascially, just because people in the USA have a particular 'received wisdom' (with very limited scientific support) doesn't mean they should mock people from elsewhere in the world who don't share their prejudices.