Why is it permissible for us to say "تلك الرسل" (those Messengers) but not "تلك الأنبياء" (those Prophets) or "تلك الطلاب" (those students) or "تلك التلاميذ" (those disciples) or "تلك الرجال" (those men)?

"Rusul" (messengers) is a broken plural, and broken plurals are treated as feminine. Therefore, it is permissible to say "tilka al-rusul" (those messengers). Accordingly, it is permissible to say "tilka al-anbiya’" (those prophets), "tilka al-tullab" (those students), "tilka al-talamidh" (those pupils), or "tilka al-rijal" (those men), because all of them are broken plurals. So, whoever mentions them in the masculine is referring to the plural form, and whoever mentions them in the feminine is feminizing the group, as if saying: "that group of messengers."