You computer can only take

You computer can only take one audio feed, so knowing this you can
A) Use 3 separate Digital Audio Recording devices, hook one lav mic to each device and record each Mic separately. Then transfer the audio file from each DAR to your computer and go from there.
B) Get a 6 or 8 Channel Audio mixer that puts the main mix out through a cable you can plug into the Audio Jack on your computer, then have it feed the audio signal directly to your Program.
B is what I have, it is an Audio Mixer, I can run multiple mics or instrument feeds into it,mix them, then send to any recording device, be a a computer or DAR.