でしょう roughly means "don't you agree" or "I agree", I didn't play the FF games so I don't have enough context to translate its original meaning here.

手に入る literally translates to "put into hand", but it means "acquire" in the context of opening a chest and finding a potion. Japanese games say "potion put into hand" and English translations say "You received a potion".

全く literally means "truly" or "very" but a lot of the time people use to mean "seriously" in a sarcastic sense. Like, "seriously!?" or "jeeze!". A beginner would think "very" but somebody with experience would know they're just complaining in a way that doesn't elicit* a response.

re: でしょう, without seeing the original Japanese, my guess is that a more atural English translation for your first example would be "Your brother is supposed to be a man, right? He's supposed to be an adult, right?" or something more along those lines.

Mato's translation comparison doesn't cover this line, so I can't easily link to the full context, but this is a young girl (Rydia) scolding an older man (Edward/Gilbert) for being too overcome with grief to take action. In the original US translation, the dialogue is "Crybaby! You are a man! You are a grown-up! You are not the only one who has lost loved ones!" The more literal translation would be "Aren't you a man?" but the meaning is the same.

"Brother" seems to be coming into it because Rydia is addressing Edward as "o-nii-chan". Pretty classic example of something that you couldn't translate accurately without knowing who the characters are.

"o-nii-chan" is a great example of translation difficulty because it's very natural in Japanese to refer to your older brother as "o-nii-chan" and it sounds like bad exposition writing in English.

And in this case it's just being used to address an older but not elderly man, in a way that's totally normal in Japanese but would be utterly bizarre in English.

(elicit, not illicit)

でしょう has other meanings in more formal use as well so your answer is incomplete