How can I convince my mom not to wait for for my ex-con, drug addict brother to come back?

You are in control. All you needed was reassurance from other wise and caring people, like you, to confirm your decisions. You are pro-active, considering all options, and have righteous priorities.
God Bless you--you are a voice of reason! We all support you here. Best Wishes to you and your family. HUGS:)

Thank you so much for your answers. I think the best thing is getting good opinions and support from people who are not emotionally involved. I can now face this issue with a clearer understanding of where mom is coming from and how to respond on her level and move forward.
I loved the idea of disconnecting the car battery! I've also called the state Hiway Patrol office and they said I could come in and sign a statement of concern. Then they would require her to take the original driving tests to re-qualify and re-new her licence. And they never reveal why. We also have an eye appt next week so her eye doc can give his opinion.
Yes, we've been to an attorney & have notarized legal papers for POA medical and financial.

You've got a tough situation on your hands, emotionally, mentally and physically. But it sounds to me like you have your priorites straight and are doing the best that anyone could under the circumstances. Try to find a way to gently let mom understand that Butch is "gone", that he won't be back in your lives, and the sweet little boy that she misses is in the past. It's all heart-breaking but you're doing a fantastic job, no one is going to thank you for it or even cooperate, but I guess you know that. remember, time is on your side here. Stay strong.

In short...I have developed a clearer picture when it comes to a messy situation due to my own life experiences. In no way I want you to think I am making light out the whole ordeal. What helps me, is to focus on the most important issues first. Mom's troubles are the true reality that is what brought you here. Obviously you care and asking for help you must realize the severity of the situation. You need to understand she may appear health but the the brain is what controls the body. Look at it this way, if you load software into a computer that has no hard ware would it be able to function? If your computer is working great than gets a virus that slowly takes away the memory would it be capable of normal function. It scares me that she is driving, people because with dementia lose depth perception, therefore a road and a curb are one in the same and what if the car should fail in some way and she ends up in a situation where she gets stressed and can't think clearly at all or hits someone and dosen't know it. The way around the taking car away is disconnecting battery, blame it on failure so your not the bad guy. I dreadfully am sorry to hear about all the pain and drama your brother has caused but Stressing about your brother or anything else is no good for anyone. Stress creates more confusion and distraction and is not good for your health. Remember that with all the confusion a person with dementia has a personal view and feelings that are deep rooted and unchangable. Your Mom deep down inside may worry about your brother because she always did because she knew he needed help. For some odd reason it is standard that a person that has dementia longs for the child that cares and whom they see the least of. A fake out may be effective in this matter, what I mean is have your other brother call her pretened he is Butch if he agrees with everything she says without making waves and has a delightful conversation she may let it go at least for a while. Put a possitive spin on the way you react when your mom speaks of Butch. As far as the living situation you should research on line the medicaid eligability in your county and state. Just be prepared to explain with proof of where all her finances and assets were spent. There is a look back period of time, In this situation it is pretty much a must to have power of attorney papers sign by her with notary. That dosen't make you financially responsable just gives you the ability to do whatever it takes to get info and documents you will need on her behalf.

You have no obligation to your Mom to help find someone who was abusive to you and other family members. Your Mom has this strange nostalgia for your brother and has painted a rather rosy picture of a really disgusting man. Stick to your guns and do not allow this person back into your life.
The stress is getting to you. Your Mom needs to be in a safe place where you can visit her and they can keep your brother from interferring. Start looking today.
Also, do you have her POAs for medical and financial. If not, do this immediately.
good luck

That is nice that your SIL told you about her wanting to find her son, and then her not helping to find this con guy. Is there anyone else she could possibly call to help her find him? Will she ask someone at church? If so, you might want to have a talk with her and tell her why he cannot come into your home. If there is no one else, maybe she will drop it? Yes, it could be she is bringing this up because it is Christmas time.