Here is a couple links we should all read to save me time in explaining some basics that REW and rePhase do.

And the link to the multi parent rePhase thread over at DIY for anyone who’s interested
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool - diyAudio

I will start gathering screenshots tonight to get into building the basics on how to make a lovely 2 seat listening position car or a down right deadly 1 seat listening position car, with standard door / dash speaker placement without minimized PLDs (path length differences) and start to jump right into it