Fa-yarmīhā contains the imperfect verb 'he throws' and a direct-object pronoun referring to Jamrat al-Aqabah. Min baṭn al-wādī describes where the action is performed.
In bi-sabʿi ḥaṣayātin, bi- is the preposition, sabʿi its genitive governed noun and idafah head, and ḥaṣayātin the genitive complement. Mithli al-khadhf describes the pebble’s character. The clause supplies action, object, location, number and description.