I am no audiophile anyone have pros and cons

I am putting a new stereo in, the new unit and 4 new speakers are 4 ohm, I plan front doors and rear floor speakers to be replaced. Is there any reason if I find 2 good original speakers that I can’t just hook the front and rear doors in parallel? The rear doors are 6 ohm.

Ignore this did some checking and it is not advised.