Why it is "dein", not " deiner" ?
Why is Eure not correct (for plural "your")
I wrote Deinen Bruder trinkt Wasser and was wrong. So I guess that means the brother is the subject?
Correct. The water is not drinking your brother :)
The answer Duo gave me is:
Eür Bruder trinkt Wasser.
with the explanation 'there's a typo in your response'. Can anyone explain the 'Eür' to me?