It is quite possible that your brother's money would be at risk under the circumstances that you describe. There really is no such thing as being a "signer only" on a bank account. If you can sign a check withdrawing all of the money from that account then you legally are a co-owner of the funds in that account. You should definitely consult an attorney for advice on the specific issues you face.
If the only connection is the checking account. Perhaps the solution is to close that account. You should consult an attorney to verify under your specific circumstances if this will resolve your brother's liability.
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