Shoplifting, Larceny, Robbery, Theft Guardianship of prisoner

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My wife wants to obtain 'guardianship' over her adult brother (about 50 y/o) who is confined in another state. He's been in jail for about one year on this latest charge (larceny), has no assets, and was recently judged mentally incompetent so felony charges against him are apparently on hold. She's convinced she should obtain guardianship to "make wise decisions on his behalf." She has nothing more specific to offer on the subject. I'm wondering if there is any benefit to doing so given the criminal case is on hold and there are no assets requiring her decision-making...