Why does the Torah see fit to inform us what those who feared Hashem did, and, in the next Pasuk, what those who did not fear Him did?
Rashi (on Pasuk 10) and Seforno: The Torah is referring to what they did by the plague of Dever, 1 and what the Pasuk means is that following the reaction of the those who feared Him there, and that those who didn't fear Him suffered the consequences, He instructed the people now to gather in their animals and slaves now or they would suffer the same fate.
Targum Yonasan: Because those who feared Hashem refers predominantly to Iyov, 2 and those who didn't, to Bil'am, 3 two of Par'oh's three counselors, who played major roles in his treatment of Yisrael. 4
See Ba'al ha'Turim (on Pasuk 17 - Peirush Yonasan.
Why does the Torah mention nor mention what the people did?
Oznayin la'Torah: It appears that Par'oh did not publicize the impending plague of hail for fear that they would panic
Oznayim la'Torah: Interestingly, 'the ice had begun to melt' and some of his servants already feared Hashem and took their animals inside. See Oznayim la'Torah.