"You guys" is simply colloquial English usage for plural "you," and doesn't translate literally. I suspect that Duolingo says "you guys" because native English speakers are more likely to associate that with the plural, whereas saying just "you" can be ambiguous. You (singular) in Irish, of course, is tú, while you (plural) (= "you guys") is sibh. Which is why you say "Go raibh maith agat" to one person, but "Go raibh maith agaibh" to two or more.
you need to understand that when you get an exercise wrong, Duolingo looks for the entry on it's list of acceptable answers that looks closest to the answer that you submitted. Duolingo doesn't understand English or Irish, so it's "closest" is just a mechanical match.
In your case, you had an extra word "don't" in your answer, so Duolingo presented you with the entry on it's list of acceptable translations that also has an extra word in that place, even though "guys" is actually part of "you guys", which someone at some point requested be accepted as a "plural you" translation of "sibh".
"You don't take your coats off" is "ní bhaineann sibh bhur gcótaí díbh"