Can Siblings Be Proxy for Their Mentally Incompetent Sister?

Yes, but not automatically, and it requires legal action through the court.

Because your sister is already considered mentally incompetent (meaning she lacks the legal capacity, or “sound mind,” to make her own decisions), you and your siblings cannot simply sign a document to give yourselves authority. You must get a judge’s permission to be appointed as her legal decision-maker.

The Critical Difference: POA vs. Guardianship

In this situation, it is crucial to understand the difference between a power of attorney (POA) and guardianship.

Power of Attorney vs. Guardianship/Conservatorship

Key Takeaway: Since your sister is already mentally incompetent, the only way for the siblings to get legal authority is by petitioning the court for guardianship (for personal and health decisions) and/or conservatorship (for financial decisions).

The Steps to Legal Authority (Guardianship)

Any sibling (or other concerned party) can petition the court to be appointed as the sister’s guardian. The process generally involves these steps:

1. File a petition: A sibling files a petition with the appropriate local court (usually probate or family court) asking a judge to appoint them as the sister’s guardian or conservator.

2. Medical documentation: The court requires medical evidence from a doctor to prove that the sister is truly incapacitated and cannot make informed decisions for herself.
    
3. Court investigation: The court will typically appoint a third party (like an attorney, social worker, or guardian ad litem) to investigate the case, interview the sister and the family, and report back on who would be the best fit to serve as guardian.
    
4. Court hearing: A judge holds a hearing to review all the evidence and determine two things:
   • Is the sister truly legally incapacitated?
   • If so, who is the most qualified and appropriate person (or people) to act in her best interest?
      

Most states follow a hierarchy when determining who will be named as an agent. While spouses, adult children, and parents are generally given priority over siblings, a sibling could be named if those individuals are unavailable or unfit to serve. The strictness of the hierarchy varies significantly from state to state and often grants the judge discretion in naming an agent who is in the best interest of the incapacitated individual.

Protecting Your Sister’s Interests

The court-appointed guardian is required to act as a fiduciary, meaning they must always act in the sister’s best interest, using her funds responsibly and respecting her known wishes as much as possible.

Important Note: Guardianship may mean a significant loss of personal freedom and rights for your sister. Courts are usually required to seek the least restrictive alternative. If she only needs help with a single issue (like managing Social Security benefits), there might be a less restrictive option available.