I DMed for the first time last night and it was great besides one aspect. I am running the lost mines campaign with two players and two NPC's (the campaign calls for four or five players, so I wanted it to be well balanced.) One player is familiar with the game, the other is fairly new. I decided and we discussed before the game how I wanted them to direct the NPC's in the party (I didn't want to have a say in the decision making, seeing as I already know the story). I was specific about it, this would only be used if they needed a specific skill from an NPC. I told them that they could try to convince the NPC's to do something, but they can't actually control the characters. I wanted them to the feeling like they solved the puzzle or they figured out the best tactic to kill the monster with the aid of their companions. I also wanted to give them "moments of glory", where they can describe an interesting spell or a killing blow when I give them the chance to. I was also rather specific about that, saying that you can describe "your" actions.
However, this had unintended results. As the campaign progressed, they became more involved in various decisions. At one point, one of the players even took control of an enemy Goblin and described its movements and actions before killing it. Occasionally, they would tell me that the NPC used a certain weapon, or that he attacked in a certain way, or the monster swung a certain direction, or reacted in a certain way. I tried to regain control throughout, but it was difficult without just saying "no" to the players. Whenever I did resort to that, the players responded with "why not?" Or "he's going to die anyway". I usually just ended up caving because it would understandably be met with disappointment. It happened rather frequently and sometimes even after I had already described the results of their actions.
I'm not even sure myself if I should do anything about it because it doesn't "technically" affect the end results. I feel as if it breaks the flow and the realism as people just throw out random results and make up crazy scenarios. Another thing that makes this feel wrong is that the NPC's seem like they aren't acting beings that have their own decision making process, fighting style and personality. They are, for the most part, controlled robots.
Is there any way to regain control over these aspect of the game without making the players feel like I'm stripping something away from them? Should I relay what I said in the beginning in more detail? Should I suck it up and let it happen as long as everyone is enjoying themselves? Or should I toss out these ideas all together and not even give them the option?