As a practical matter I would take the position that all the equipment you were the signer on was a loan and that you want the loan paid off in full. Failing that you will take the equipment. Shut down the business and open it under another name with just you and your wife as owners. Tell you customers that you are leaving the business and leave it up to them as to where they want to go.
This approach is on the legal edge but I doubt that your brother in law or the mother have the wherewithal to fight it.
It is very difficult to have a person declared incompetent. That would be a very time consuming process and even if successful, you would have to deal with the person appointed to govern her affairs. If you think she is not competent, you should retain an attorney as we only provide general information and not legal advice.
DISCLAIMER: Answers from Experts on JustAnswer are not substitutes for the advice of an attorney. JustAnswer is a public forum and questions and responses are not private or confidential or protected by the attorney-client privilege. The Expert above is not your attorney, and the response above is not legal advice. You should not read this response to propose specific action or address specific circumstances, but only to give you a sense of general principles of law that might affect the situation you describe. Application of these general principles to particular circumstances must be done by a lawyer who has spoken with you in confidence, learned all relevant information, and explored various options. Before acting on these general principles, you should hire a lawyer licensed to practice law in the jurisdiction to which your question pertains.
The responses above are from individual Experts, not JustAnswer. The site and services are provided “as is”. To view the verified credential of an Expert, click on the “Verified” symbol in the Expert’s profile. This site is not for emergency questions which should be directed immediately by telephone or in-person to qualified professionals. Please carefully read the Terms of Service (last updated February 8, 2012).