Condolences.
How that works out depends on how well you get along with your siblings.
I see two possible ways to handle this (there may be more).
Let's assume that the car is worth $10,000 for this illustration.
1 - You pay $10,000. The $10,000 goes into the estate account. The car is deleted from the estate's assets. The estate is still worth what it was before the sale of the car.
2 - You pay $7500 for the car. $2500 you keep as an advance on your inheritance. When the estate is settled the $2500 is deducted from your share.
Zigner makes a good point. Number 2 works if there is more than enough cash or liquid assets to pay all the debts and expenses of the estate. If there isn't then the car may have to be sold to pay creditors.
Again, depends on how well you get along with your siblings. If you all get along well and agree on KBB, then go with that. If somebody objects, check Edmunds and NADA price guides for used cars and take an average. You can also look for comparable cars on Craigslist and Auto Trader, understanding that selling price is often 10% or so below asking price. You shouldn't need to spend money on an appraisal unless there's some real hostility going on between siblings and/or the probate court orders it.