Let me state from the beginning that I do not own stock in, work for, nor have any relatives who do the same for Crutchfield. Have used their products for over 20 years on 4 different vehicles with excellent results & fantastic customer service. As always, use your own judgement as to your purchases.
If you pull off the door panel & the remove the OEM speakers, I think you'll not see any separate crossovers.
Kicker 46CSS654 CS Series 6-1/2" component speaker system at Crutchfield shows separate crossover. Crossover has 3 leads clearly labeled: input, mid, tweeter. Connect OEM lead from radio to input, then connect tweeter & mid outputs to correct speaker. Tie OEM tweeter wire to OEM tweeter lead. then tie Kicker tweeter lead to same OEM lead to keep it neat. Should have no problem using electrical ties to attach crossover to inner door frame. Use more ties to create neat, uncluttered look.
If you are replacing speakers, I have 2 other suggestions:
1.] add some sound deadening material of your choice to the inner door frame and to the inner door surface. After you remove the inner panel, carefully remove the plastic weather seal. Keep the sticky stuff separate from other parts of this film so that you can reapply the weather seal when finished. Carefully wipe down the inner door surface and apply your sound deadening material. I found using trim removal tools helped create a tight bond between the metal and the sound deadening material. How much further to go into sound deadening your vehicle is up to you.
2.] a small amp, somewhere along these lines
kicker amps at Crutchfield. will greatly add to your audio enjoyment.