The brothers, while unnamed, certainly included Laman and Lemuel at the minimum. Whether or not Sam was involved is unknown. When Nephi asks the cause of their discussion, they answer that they do not understand the reference to natural branches of the olive-tree (see 1 Nephi 10:12-14). Having the advantage of the Book of Jacob (not written at this time) we know that there is a much larger context for this reference. We also know that it is a long allegory written by the prophet Zenos (Jacob 5:1) and contained on the brass plates.
We know that Lehi had read at least some of the plates, and it is probable that he had read them all, and therefore the image of the allegory of the olive tree would be a ready reference for Lehi.
It is just as clear that neither Laman nor Lemuel had read the Zenos section of the brass plates, or else this would not come to them as such a mystery related specifically to their father's vision. Both in lack of general understanding and lack of preparation, Laman and Lemuel were unable to answer this question.