I am not sure my long post reads right. If you follow it, this is what happens:

The rear left speaker output line of the Kenwood drives the amp which then drives your new speaker in the driver's door and the speaker behind that seat.
The rear right speaker output line of the Kenwood drives the amp which then drives your new speaker in the passenger door and the speaker behind that seat.

The front left speaker output line of the Kenwood drives the driver's tweeter directly.
The front right speaker output line of the Kenwood drives the passenger's tweeter directly.