You can wire your door speakers in parallel with your dash speakers. That amp can handle a 2 ohm load so your fine there. Make sure to
put some kind of crossover between your 6x9s and your 3.5 inch speakers tho because the 6x9s can handle a lot lower frequencies than the 3.5 inch speakers. if I could make a recommendation tho I would put some components in the front instead. Put the mid range in your doors and mount the tweeters up in the dash. If you have 6X9s up there and 3.5s and they are both coaxial speakers that's 4 tweeters and it's gonna be very overpowering on the higher frequencies.