As far as I know, atem is for addressing a group of males or a mixed goup with at least one male. aten is for a group of females.
In English, some use "you guys" to address a group of girls, too.
You can definitely interpret it, personally, as "you guys" provided you're aware males and females are addressed differently in Hebrew. I wouldn't go as far as trying "y'all" on Duolingo, though.
Arabic Influence: Modern Period
Author(s): Henkin-Roitfarb, Roni
The impact of Arabic on pre-modern Hebrew, most prominently on the Hebrew of the Middle Ages, is well documented. This entry surveys the influence of Arabic (literary, Palestinian, and Jewish Moroccan) on Modern Israeli Hebrew from the 1880s. Two routes of adoption are discussed: planned coining and spontaneous borrowing. Sometimes these routes overlap, i.e., when spontaneous borrowing is standardized retroactively. 1. Pre-State Contact In late 19-century Ottoman Palestine, where Modern Israeli Hebrew emerged as a spoken language, Palestinian Arabic was the…
Source: Encyclopedia of Hebrew Language and Linguistics
Hebrew and Arabic are two languages in the Semitic family. There are other languages in the family, past and present, and you're likely to find this root in several of them. The history of the family began even before the any part of the bible was written... If you see similar words in the bible and in Arabic, chances are both Hebrew and Arabic inherited it from some common ancestor language.
I read an online discussion somewhere (I can't remember where) recently where people were discussing how they didn't want to sound stupid by learning Hebrew using Hebrew Academy pronunciation. Do you know what they meant by this? Would it be because they wanted to sound more (how should I put this?) "street"? Less formal?
It's a common trait thought by language learners (about their non-native language). The more comfortable you are the less likely you'll think it. (Unless it's me, Ben Shapiro, or micro machines guy John Moschitta, then it really is fast).
See more about this here: https://www.psychologytoday.com/us/blog/life-bilingual/201302/why-are-they-talking-so-fast