If it is a simple spreadsheet I'm sure if you Google you can find PHP scripts that can edit them. This way when your parents edit the data in their web browsers, you too can edit the data from your web browser.
I believe Excel in Office 2007 still uses Comma Separated Variables (CSV) which easily allows the data to be edited. You could easily convert the data to fit into a MySQL database, which you could download/ upload once changes are completed
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It sounds a more complicated approach, but it is the only thing I can think of.
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