As you correctly state, this passage relates entirely to the disposition of endowments dedicated to charity. In it Bahá’u’lláh provides that the authority in this matter passes, after Him, to the Aghṣán. The Aghṣán comprise not only the sons of Bahá’u’lláh, but all His male descendants. Thus in His Will and Testament ‘Abdu’l-Bahá refers to Shoghi Effendi as “the chosen branch,” and provides that if the eldest son of the Guardian did not possess the qualities which would befit him to be appointed as his successor, the Guardian should “choose another branch [Ghuṣn] to succeed him.” There is also a letter in which Shoghi Effendi refers to his brother, Ḥusayn, as a “Ghuṣn.”
It should be noted that, although only two of the Aghṣán are explicitly mentioned in the Kitáb-i-‘Ahd (the Ghuṣn-i-A‘ẓam and the Ghuṣn-i-Akbar, namely ‘Abdu’l-Bahá and Mírzá Muḥammad-‘Alí), paragraph 42 of the Aqdas refers to more than two. Arabic nouns have three forms for number:
|Plural||more than two Branches||Aghṣán|
The Aqdas foresees a hereditary function for the Aghṣán in relation to the disposition of endowments dedicated to charity. Paragraph 42 of the Aqdas continues by stating that “after them” [i.e. the Aghṣán] this authority passes “to the House of Justice—should it be established in the world by then.” This envisages the possibility that the line of Aghṣán would come to an end before the Universal House of Justice came into existence, which is, in fact, what happened on the death of Shoghi Effendi.