Importing music mp3s into a main .aup project

I use Audacity 2.x with a Mac Air using Mac OS X 10.9.4
I have a problem with importing music mp3s into an existing .aup Audacity project. The project is an interview into which I have previously successfully imported short verbal clips recorded directly through the Mac Air’s internal microphone. Each appeared as a new tracks beneath the main track which I could then cut and paste into the main track.
When I use File/Import/Audio to import a music mp3 a) The mp3 does not appear within the project as a separate track beneath the main track b). It is mixed with the very beginning of the main track. It does not mix with, or appear beneath, the main track at the point where I positioned the cursor. c) Because it does not appear as a new track, I cannot cut & then copy it into the main track at the point where I want it heard, that is after where it is mentioned in the interview. d) When I import a second mp3, it joins the first at the beginning of the main track, so the two mp3s are mixed simultaneously with the main track! e) Finally, the music is much louder than the interview/main track and because they are already mixed, I cannot find a way of adjusting the balance.

To sum up, I would prefer to place the music clips separately within the main track, to illustrate points made in the interview, rather than have them mixed as background to the interview, although this will serve if the first model is not achievable.

The main issue seems to be, how do I import music mp3s into the main track at the points which I choose?

Please don’t double-post. I’ve answered this same question in your other thread.
– Bill