Detailed answer — what Michigan law and practical steps say

1. First, identify the account’s legal status

Your legal options depend on how the account is titled:

• Solely in the decedent’s name: The account becomes part of the decedent’s estate at death. No one (other than an authorized representative or someone properly appointed by the probate court) may lawfully spend funds for estate administration without authority from the court or pursuant to a recognized exception.
• Joint account with right of survivorship: A surviving joint owner typically becomes the owner automatically and the funds are not part of probate. In that case, the sibling may have a lawful right to use the money.
• Payable-on-death (POD) or beneficiary designation: Funds pass to the named beneficiary and usually avoid probate; the beneficiary can claim and use the funds.

Where to read Michigan law

Michigan’s probate statutes are in the Estates and Protected Individuals Code (EPIC), MCL Chapter 700. You can read the chapter here: MCL Chapter 700 (EPIC). Michigan courts oversee probate matters; general probate information is at the Michigan Courts website: courts.michigan.gov.

2. Common bank reactions after a death

Banks typically ask for a death certificate and may freeze or restrict access to a decedent’s accounts. Policies vary. Some banks will continue limited disbursements for bills (mortgage, utilities) if a person claims to be handling estate affairs, but many will require proof of authority (letters testamentary/letters of authority) before allowing ongoing withdrawals.

3. Can you challenge your sibling’s withdrawals before they are appointed administrator?

Yes, you can challenge unauthorized use, particularly if the account is solely the decedent’s or you reasonably believe the sibling lacks authority. Practical and legal options include:

• Inform the bank in writing: Provide a copy of the death certificate and request the bank freeze the account or place a hold pending probate. Ask for a copy of the bank’s policy in writing.
• Gather documentation: Collect statements, copies of the mortgage statement, proof of ownership of the property, and any communications showing the sibling’s withdrawals.
• Demand letter: Send a written demand that the sibling stop using the funds and preserve records. Keep proof of sending.
• File in probate court for emergency relief: You can ask the probate court to temporarily prevent wasting estate assets and to require an accounting. If estate assets are being dissipated, many courts will entertain emergency petitions to preserve funds until a personal representative is appointed.
• Seek appointment or an expedited appointment: If you want to control the estate administration, you may petition to be appointed personal representative. The court can grant temporary powers or prioritize appointment in urgent situations.
• Consider civil or criminal remedies: Unauthorized use of funds can support a civil claim for conversion or unjust enrichment. In extreme cases, theft or embezzlement charges may be possible; you may report suspected criminal activity to law enforcement.

4. What the probate court can do

The probate court can issue temporary orders to protect estate assets, require an accounting, and appoint a personal representative. If a sibling is taking money without legal authority, the court can enjoin further withdrawals and require restitution as part of the probate proceedings. Use the probate petition process to bring the matter before the court quickly.

5. Typical timeline and evidence to prepare

Act quickly. Practical timeline steps:

1. Immediately request account freeze and collect records from the bank.
2. Gather death certificate, bank statements, mortgage statements, and correspondence.
3. File a probate petition asking for appointment or emergency protection — some courts schedule emergency hearings within days depending on the situation.

6. What if the sibling claims mortgage payments are “in the estate’s interest”?

Mortgage payments may benefit the estate by avoiding foreclosure and preserving the asset. A court will weigh the need to preserve the property against the risk of improper use. That is why the probate court is the proper forum: it can authorize reasonable expenditures for estate preservation while protecting against waste.

7. Practical considerations and risks

• If the bank allowed the sibling to withdraw funds, the bank may be liable to the estate if it released funds without proper authority — ask the bank for its written basis for release.
• Being confrontational with your sibling can complicate resolution. Use written demands and court filings rather than heated personal disputes.
• If the sibling is a joint owner or a named beneficiary, legal ownership may not be contested; your remedy may be limited.

Helpful Hints

• Obtain multiple certified copies of the death certificate — banks and courts will ask for them.
• Ask the bank for a written explanation of why it allowed withdrawals and for copies of any withdrawal slips or authorizations.
• Keep careful records: dates, amounts, and any communication (texts, emails, letters) about withdrawals or mortgage payments.
• Consider filing for appointment as personal representative if you want control over estate decisions; the probate court can consider emergency requests to prevent asset dissipation.
• Use the probate court — it has tools to freeze assets, enjoin unauthorized conduct, and order restitution.
• If the dollar amounts are small, ask the court about simplified procedures or small-estate options; if large, prepare for a formal probate proceeding.
• Talk with an attorney who handles Michigan probate and estate litigation if you anticipate contested hearings or potential criminal conduct; many offer free initial consultations.
• For general Michigan probate information and forms, visit the Michigan Courts site: courts.michigan.gov.