What is the correct interpretation of the story of Harut and Marut, and is the reading "al-Malikayn" (the two kings) with a kasra on the lam correct, implying that they were human beings and that their description as kings was based on the belief of the Jews?

The reading of "al-malikayn" (الملكين) with a kasra on the lâm is a shâdh (aberrant) reading and not among the ten mutawâtir (concurrently transmitted) readings. Al-Jassas reconciled between the two readings of "al-malikayn" with a fatḥa on the lâm and with a kasra. For those who read it with a fatḥa, he considered them to be angels. For those who read it with a kasra, he considered them to be non-angels. He clarified that both readings are correct and not contradictory. It is possible that Allah sent down two angels during the time of these two kings (who were humans), due to the widespread practice of magic in their era. It is also possible that the two angels who were sent were tasked with informing the two human kings (and their followers) about the reality of magic.