The first one might be better if it said 'for all of you guys' If you are doing the pouring, why would you ask others to pour you a cup?! :-)

I have to disagree with the other correction. I have never in my life heard 'I'm pouring you guys some cups of coffee." I think either are fine for conversational purposes. I understand his point about the the number of people versus the number of cups, but I think most people would get the idea. You could say, I'm pouring you guys some coffee. For example, it there was a group of people at your house, you might say, "Do you guys want a beer?" Obviously they are not all going to drink the same beer--that is understood. But you would not say, "Do you guys want some beers."

FYI, I'm not a teacher though I am a native English speaker. To be candid I think the first one is incorrect. The second is an improvement, though I don't think it's correct either. The first one states you are pouring one cup of coffee for all of them. This suggests they need to share one cup between them all. The second leaves some doubt about what to you mean (in my mind at least). An you might be able to use it... Though, I don't recommend it. I suggest... "I pouring you guys some cups of coffee. Could you pour me a cup as well." (Though I question why they need to pour you a cup of coffee as you are the one doing the pouring. I assume that's not important).