You can say όχι αυτοί οι άντρες (and it is an accepted answer/if it was not accepted for you, please let us know) if you answer to a question that used "these men" in nominative (usually as a subject of the sentence):
-Αυτοί είναι οι άντρες για τους οποίους μου μίλησες; (are these the men that you talked to me about?) -Όχι, όχι αυτοί οι άντρες.
But if the question used "these men" in accusative, you have to answer in accusative (usually as an object of the sentence):
-Αυτούς τους άντρες ψάχνεις; (Are you looking for these men?) -Όχι, όχι αυτούς τους άντρες.
ahhhh I understand now. Okay thank you for that clarification. Also I do duolingo on my computer so I turned off the exercise where you match the words to answer, I set it up to where I type everything and it didn't accept my nominative answer. Thank you again for taking time to answer my question!
Hmm, well, I (and, based on the comments, others as well) seem to have had similar experiences with other questions too. I am at a loss as well- I suppose there are just some glitches. Anyway, I really only care to know that I am understanding what I do correctly and incorrectly so that I learn well, so don't stress about it.
Re: nominative vs. accusative, this sentence is almost a fragment (although here it's a complete answer to a question.) It depends on what the question was: "Did these men kill our goats?" The answer would be in nominative because "these men" is the subject of the sentence. "Which men will we draft into the army?" would have the accusative answer, since "men" is the object (we will draft men.)
You can't always tell which will be the correct answer. However, I like Duolingo's use of fragments, since sometimes we learn to speak in segments. And the ambiguity makes us pay attention to the difference between nominative and accusative. (It's kind of fun to make up sentences to fit.)
No. Άνδρες is the older form; formal language used mainly in written speech. If you do pronounce it however, it sounds much softer than άντρες and in oral speech it might even be humorous for "effeminate men," especially if you wink when you say it. (th δ sounds softer than d ντ) Ηope I helped a bit. :)