Those door speakers seem excessively more powerful than any headunit can possibly drive. A lot of tweeter kits come with adapter brackets to fit into numerous factory spaces.
Are you replacing the speakers placed in the dashboard panels up top? or putting it into the bracket where the door speaker is? This doesn't seem like a logical position for those speakers, with or without an amplifier you will most likely see reduced sound quality with a tweeter being in the same position down by your feet. You are better off changing out the speaker in the dash.
If for whatever reason your car didn't come with speakers in the top mount location, its best you add them there.
Sonicelectronix.com has been my go to place for car A/V stuff and they have a great selection and tons of properly categorized info. If you don't plan on getting a dedicated amplifier for this, its best you keep the RMS under 20watts. The headunit will probably send about 15-25watts rms at best.
Not sure if this site still offers these adapters, but here is what is listed to get the job done.
PVC Speaker Adapters - CNC Machined - In Stock or Custom Made
purchase according to the size tweeter you plan on getting.