I thought I covered all that, I guess I should have not said anything else other than, do not place tweeters on the door sail panel. No rears to me sounded like the OP wanted to bi amp, if the OP is set on the sail panels then I wasted some time posting, but based on the OP's last post he wants to mount them on the dash A pillar.
Sail panel tweeter placement and bi wire bi amping will be difficult and time consuming.
An extra line of speaker wires will be needed regardless, the factory wires can be used for the tweeters or the woofers, for convenience or preference.
The OP mentioned no rears, maybe 2 channels will be wasted or disconnected? why waste 2 channels? bi amp the components or use them for rear fill controlled reduced ambiance, even with the factory speakers.
The passive crossover from the Morels or the Focals PS I mentioned offers 2 options as compared with 99% of the rest of components on the market that their passives only use 2 channels to drive both tweeters and midwoofers.
With those PS Focals the Op has these options.
1. 2 channels for the woofers and 2 channels for the tweeters, amplified.
Or
2. Use 2 amplified channels for just the components, maybe bridge a 4 ch amp to power them, or use the other amp channels for the rears, or use the HU power for the rears, he can also just use the HU power for the tweeters and it's crossovers, bridge a 4 ch amp, just for the mid woofers.
Many options and the information on how to install and connect them has been posted already.
Some extra information about tweeter placement.
By having them on Axis on the pillar dash area some windshield reflection is prevented, and the harsh effect will not be as bad as having them on the sail panel, since mine offer laid back sound they worked well there. A bright tweeter may need to be EQ down, installed off axis or moved to a different location in some cases. Increasing the slope will smooth out and reduce the bright and harsh sound, but then again, they need to have their pair of independent channels , in order to make the slope more effective assuming the HU offers those options or a Sound processor is used.
I guess I am done posting on this thread. I hope someone benefited from some of the information and time spent.
OP Feel free to PM me if extra help is needed.
Other than pointing out the function of HU electronic filtering and external processors supporting all kinds of DSP, I'm not quite sure what the point of all that text is, but... in reference to bolded content above, there is a lot of confusion, or perhaps those words were misconstructed, hence confusing.
Crossovers, whether passive of active ARE filters. Other than dynamic adjustments, there is only one difference between active and passive frequency division - and that is amplification before or after filtering takes place. Passive crossovers don't "need" a HP filter, passives ARE filters operating at fixed upper, lower or band pass frequencies and attenuation slopes.
If you are taking about home speaker crossovers maybe, but most car passive crossovers for the woofers are just a Low Pass, therefore sir, they do need a High pass from either the HU or the amplifier. No misconstructed or confusing words here.
If you dont use a HP, either from the amp or HU, the 6.5 cone will try to play below 80-70 hz down to 20Hz and that is potential death or more excursion and distortion. That is why components play more bass when no HP is used, way more bass than we want to hear and at loud levels the bass gets impossible to EQ or reduce for ideal sound. Been there done that already.
With the HU HP at 80 hz, for example, the safe frequenccy range for the 6.5 woofer will be 80 to 2800Hz for example, and from 2800hz and up is up to the tweeter to play those frequencies. Either with a passive or no passive a woofer needs a High pass and it is safer for it to try to play above 2000 Hz, it will cause beaming or overlapping but safer than when you let a small tweeter play below 1000 hz and kill it.