(1) ANMELDEN can mean to "sign up" or "log on" or "sign in" (like onto a website), as well as register or enroll. Offline, it's more like "sign up" but less formal than "registrieren".
(2) EINTRAGEN is more like "fill out" or "put down," so it can also mean to enroll or sign up, but its more like putting your name down on a list.
(3) REGISTRIEREN: Mostly used online for "sign up and create an account". Offline, it sounds quite formal and wouldn't be used if you sign up for a sports club. But it's kind of popular to use it in a passive way: "Ich habe mich registrieren lassen." (as an organ donator or something similar).
Thanks to @UclaBruins12 and @pseudocreobotra for answering this in a previous post.
Because that's not a translation of Wir werden uns anmelden.
To report something can be etwas melden, but this sentence does not use the verb melden, it uses sich anmelden.
(Even if the sentence had used sich melden, that would have been different from non-reflexive melden.)