Don't get hung up on the translation. Etc is an English word, and its Latin origin does not tell you everything about how it is used.
In Latin, cetera means "the rest", or "the other things (in the known or implied collection)". alii means "others", and is masculine plural, so it could apply to any things which happened to be masculine in (grammatical) gender, but in particular would apply to people. "Other things" in Latin would be alia.
In English, etc (read, and occasionally written, as et cetera) means "and so on", or "and other things of that type". Et al. (which is almost always abbreviated that way, even when spoken) usually means "and other people", and is used in referring to academic papers by more than two authors: I don't believe I have ever seen it used in any other way.
The Latin phrase et alia ("and other things") might be used in English, but I don't believe I've ever encountered it - unlike inter alia ("among other things"), which is fairly common in academic English.