You can certainly see why individual interpretation went astray! I'm a translator, btw, and determining exactly how a word is being used is a very difficult task, even in modern languages. You have to get it from context, that is, both the context of the document (which is often useless) - and the context of your knowledge of the culture, the issue in question, the conditions surrounding it, and what you have learned from speaking that language and traveling in that country. In other words, even in modern translation, you're relying on "tradition" to give you an accurate understanding of written words.
The NAB gives this commentary on Mark 6:3
The brother of James . . . Simon: in Semitic usage, the terms “brother,” “sister” are applied not only to children of the same parents, but to nephews, nieces, cousins, half-brothers, and half-sisters; cf Genesis 14:16; 29:15; Lev 10:4. While one cannot suppose that the meaning of a Greek word should be sought in the first place from Semitic usage, the Septuagint often translates the Hebrew ah by the Greek word adelphos, “brother,” as in the cited passages, a fact that may argue for a similar breadth of meaning in some New Testament passages. For instance, there is no doubt that in v 17, “brother” is used of Philip, who was actually the half-brother of Herod Antipas.
tortured by any standards