You are going to need an interface between the mic and head phones of some sort. this is to amplify the mic signal for head phone playback. so Microphone to preamp-amp out to two head phones, could use a y splitter here from the output of the amp to the 2 head phones. so yes you do need a mixer or preamp-amp to drive the mic and the out put.
no way around it.
If you tell us what your actually trying to do with details on what equipment you have then we could give a more detailed reply. right now all I think you have is a mic, y-spliter and two head phones.