Equipment needed to record sound when filming an interview with two people
You could simplify your costs and needs with this approach to your kit:

Get a similar unit to the Alesis PalmTrack to record your audio, preferably on 2 channels, or as a pair of Left and Right inputs from suitable microphones.
Monitor your Left &amp; Right balance with suitable headphones to ensure the usual clean, distortion free audio.
Later, you could remix your balance levels in Audio Editing software between the 2 Mic inputs. 
This would effectively eliminate the cost for the separate Audio Mixer, &amp; the "live" audio mix.

Another solution could eliminate the need for 2 separate mics:

For any interview between 2 people, a pair of mics is almost always necessary.
However, if the camera shot and setup allows, you could park your Audio recorder on the end of a "fish pole" or "boom" attachment, and hold this over your subjects, out of shot, to record the conversation. A bit of practise and skill is required for this to be successful. 
You do have to avoid the noise of handling the boom, as you 'pan' or 'swing' the recorder mics in the direction of either speaker.

Another alternative would be to park the recorder above the 2 persons, just out of shot and record audio from there. Correct positioning and minimum body movement of the subjects for the duration of the recording would be critical, however. Best done by seating both at a table, or similar.

A look online at some setup examples, like the searches below might help to visualise a rig:

https://www.google.co.uk/search?q=Film+interview+audio+setups&amp;tbm=isch

https://www.google.co.uk/search?q=Film+interview+setups&amp;tbm=isch