The dealership is just a responsible as your brother. More so, it sounds as if the dealership committed an act of fraud knowingly, 1) dealing with a person who was intoxicated or not of sound mind to make rational decisions, 2) trading in a vehicle that does not belong to buyer and 3) accepting the sale knowing it is not correct (this one you will have to prove beyond a reasonable doubt).
Under, KRS 367.220 statute, if you can prove that auto dealership committed fraud, you are covered under the Consumer Protection Act. You might be able to revoke acceptance of the vehicle under the Uniform Commercial Code (KRS Chapter 355). You will need to contact the Office of Attorney General to file a claim under the Consumer Protection Act http://ag.ky.gov/.
There is no statuory right to cancel the "sale". Unfortunately, Kentucky has no USED CAR Lemon Laws but they have rights to consumer against vehicle fraud.
You can file a complaint with the Attorney General's Office and with the Kentucky Motor Vehicle Commission in Frankfort. Remember neither agencies represent you. If you have more questions, I suggest you seek the advice of a licensed attorney in Kentucky.
Now, can you keep your brother out of trouble next time? :-)
Thank you and Good Luck!