To get an interdiction, you'll need to prove that your family member is unable to make reasoned decisions about their own care and property.
It is your responsibility to give clear and convincing evidence. Other people can help you!
These professionals can provide their expert opinions of the interdict's abilities:
Each of people who help you should have experience in evaluating an intellectually disabled person and experience working with your family member.
Sources: LA Code of Civ. Procedure art. 4548; Succession of Fisher (2007).