Are Harut and Marut two men or two angels? And is the reading of "malikayn" (two kings) instead of "malakayn" (two angels) from Ibn Abbas authentic and supported by evidence?

The correct interpretation is that the verse, "And what was sent down to the two angels (al-malakayn)" — with an open "lam" (la)— refers to Harut and Marut. They were two angels whom Allah sent down as a trial and test for humanity, and He permitted them to teach magic.

Al-Tabari favored the view that Harut and Marut were angels, not humans, because Allah denied that Solomon, peace be upon him, practiced magic. Furthermore, they would say to anyone learning from them, "Indeed, we are a trial, so do not disbelieve" [Al-Baqarah: 102]. This indicates that they forbade magic, rather than commanded it.

As for the reading "al-malikayn" (the two kings) — with a kasrah on the "lam" (li) — it is an irregular (shadhdhah) reading, not mutawatir (continuously transmitted), and its interpretation suggests it refers to David and Solomon, peace be upon them.

The correct view is that Harut and Marut were two angels whom Allah permitted to teach magic as a trial, and they advised the learner not to disbelieve.