[NYer]

As you can see, the NT writers did know how to refer to someone as cousin or kin, instead of brother.

You are quoting an English translation! Look at the original Aramaic form.

[Mr Rogers]

I am quoting english translations of Greek. Greek DID have a word for kin (syggenes) or cousin (anepsios), and it WAS used regularly by NT writers, including Luke.

As for Aramaic - look it up in a lexicon. But don’t forget - the Holy Spirit used Greek in breathing the NT scripture.