A Final Account of your mother-ine-law's Estate details every transaction that has occurred during the Estate of your Mother-in-Law. Instructions for which are set forth on the Chester County Orphans' Court website, the general details of which begin with Rule 6.1 and continue through the rules. In short, the filing of a "Final Account" includes an Accounting (which must follow the Court's forms - general accounting software such as Quicken, etc., is not sufficient); Receipts and Releases from all Beneficiaries; information regarding the Payment and Satisfaction of all estate and inheritance (i.e, "death") taxes, fiduciary taxes (i.e., "income taxes" of the estate), and creditors; and an Affidavit by the Executor that he has filly and completely satisfied his duties as Executor. Further, a Status Report stating this information must also be filed. Please always remember that if anything is left undone or incomplete, your husband will be held personally responsible for any errors, shortfalls, and mistakes. It is the duty of the Orphans' Court to monitor these things.
I truly hope that I did not overwhelm you with my explanation. I live and work in Chester County, PA, and although all of this "legal" stuff can seem overwhelming, with a little explanation and further instruction, all of these pieces fall into place quite nicely.
Depending on the complexity of the estate (number of assets, etc., number of transactions) the filing of the accounting can be a bit beyond most non-lawyers or non-accountants. A lot of accountants don't even know how to properly do one. Just to get started you would need a complete inventory of all assets, all debts, all transactions to all accounts, etc. I recommend hiring an attorney. Chester County is a bit far out for me to go to but I can recommend someone who can handle it.
My recommendation is that you have all the beneficiaries sign a family settlement agreement with a copy of the first and final account attached thereto and file it with the Register of Wills. The alternative would be to file the accounting with the Court and have it approved at "audit". There are model accounts available but even with a form you may find the process difficult. The advice to engage an experienced lawyer to handle the finalization of the probate administration is good advice. I am in Downingtown and would provide you with a free consultation to elaborate.
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