If I remember well, Detering (or Stuart for that matter) thinks that the passage was an interpolation, one meant to consider Paul as one who, afterall, didn't despise the pleasures of the flesh (as the marriage), contra Marcion's despise of marriages.
Therefore, even if that passage was an interpolation, the meaning of ''Brothers of Lord'' remains not changed in my view: they are the Christian hoi polloi (carnal people).
Did Acts invent a James brother of Jesus who was ALSO a leader?
Re: Did Acts invent a James brother of Jesus who was ALSO a leader?
Nihil enim in speciem fallacius est quam prava religio. -Liv. xxxix. 16.