[brisboats]

If you friend's brother is the executor of the estate do what David says act as his advisor/ pro bono assistant. Have him create a user ID on Bat and be the seller of the car for the estate. You can chime in and even answer questions for him in the comments section. I am sorry to hear about your friend and think it is great you want to help and be involved. You just need to protect yourself. At the moment you have yourself, your deceased friend's brother and the 993 buddy involved. So as with any transaction the odds of difficulty increases with the number of parties involved even when all seemed amicable from the beginning. The larger the $$$ value of the transaction coupled with emotional sentimental attachment are denominators for more problems.
You asked what would I do. I'll can tell you that I would not sell the car with my user ID. Because Jacob was a friend I would help and offer assistance like you are pro bono. Every State has laws regarding the sale of motor vehicles and laws regarding trusts and states. I would do some research with your State DMV and registrar of wills. The depth of that research would be determined by if $$$ was coming into my hands or office accounts in anyway be it escrow, commission, tip, anything.
B