My brother is mentally challenged and lives with me. I have been taking care of my brother. There are a couple of properties in my brother’s name and I manage them for my brother. Can he transfer those properties to me by making a will in this regard?

In Mississippi, a person who is of unsound mind or an unemancipated minor is considered incapable of making a will.  The question is whether he is considered incompetent.

You would need to file for a conservatorship to take care of his property.