I am the executor for my brother's estate. I have an estate bank account set up and have been taking care of the debts that remain. My question is this: Can some of the money be used to purchase a car for his son?

I would say NO. But check with your attorney.
Homer

The cash in the estate can not be used to buy a car for the son, unless the estate has been settled and the remaining cash has been disbursed to all of the heirs. Then, the son can use the cash to buy a car.