Manny, I'm so sorry mate. I really I am, I went through similar thing when my dad was murdered couple of years ago.
You've got a tough call to make. I agree with sentimental value, it's your dad's car on the end of the day. I do really like idea of selling both cars and buying better/newer D3, maybe more economical if that bothers you, and because it's partially bought from your Dad's car money, you will keep that sentimental value with new car. It's not the same what driving his car, but driving an A8 it's not the same what driving Fabia.
Another thing, you've got two A8s, there is a good reason I believe why you've chosen cars from the executive range not hatchback.
If you wanted a hatchback you would have one, but not comfort and class is most important for all the people, sometimes sentimental value beats it all.
Remember, there is nothing wrong with selling the car and using the money to buy a newer or better one, ask yourself if your Dad would mind it or not.
Tough call as mentioned earlier, but you've got to go with your instinct.
Whatever you decide it will be the right choice
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2006 D3 S8 5.2 V10
Ceramic Brakes, Bang&Olufsen, DTV, DAB, Rear Camera, BT, TPMS, Soft Close, Auto Boot, AMI , 4 Zone AC, Home Link, All Electric Blinds, Fingerprint, Ski Hatch, Black Extended Leather, Heated Sport Seats, Alacantra, Carbon Trim inc Aluminium Pack 2.
2015 A3 S line 1.4 TFSI - for the missus to keep her away from my car.
Standard S-line equipment, no extras.
2006 D3 A8 3.7 V8 - SOLD but not forgotten