"Do you all see me?"
Translation:Seht ihr mich?
"Do you" could address one person or several; "you all" is used to clarify that the second is true so the 2nd person plural "seht ihr" is to be used, not the 2nd person singular "siehst du". An english sentence specifying "every person in a group" would probably be more like "can everyone see me?"
Rubbish. In English the sentence would be 'do you see me' which would refer to both singular and plural (unless you are a redneck American). So in German the sentence is correct with the meaning referring to more than one but in English you would not say 'do you all see me'. It's an awkward sentence.
I agree. In view of the problem caused by "you" being both singular and plural in English, when giving us an English sentence to translate into German, it would be better to put something like: "Do you (plural) see me?" rather than adding an extra word "all", which then gets marked wrong if we try to translate it. I've just had the German sentence to translate into English, and it rightly accepted my answer, "Do you see me?" (without the "all")
No. sehen is a normal transitive verb and takes a direct object in the accusative case, so the dative case mir is wrong.
Also, "you all" here is intended to be plural "you", so du is wrong -- it has to be ihr when you are speaking to multiple people.
And sehst isn't a correct verb form anyway. For du, it's du siehst (with a change of vowel); for ihr, the verb form is seht.
So none of those words in the sentence were correct, unfortunately.
euch is the accusative case -- you would use it when it is the direct object of a verb, or after certain prepositions.
ihr is the nominative case -- use that as the subject of a verb.
It's a bit like the difference between "she" (subject) and "her" (object).
Seht euch mich? would be a bit like saying "Does her see me?"
English "you" and "it" don't distinguish between subject and object forms, but the other pronouns do -- so try substituting one of them if you're in doubt.