A hypothetical situation.

Imagine a man dies and leaves his money to his grown kids.  The kids are later at a Thanksgiving dinner with extended family, and their great-aunt says something about how their father had an offshore tax haven in Switzerland and hasn't paid taxes on his FULL income in ten years.

According to moral theology, would the children who have inherited the money be obligated to investigate this information just based on the hearsay, and then make reparation if it turns out to be true?  Or can they simply leave it alone until proof smacks them in the face in the form of an audit or what-have-you?

And if making reparation would utterly ruin them, would that change matters, especially since tax laws are very draconian and charge enormous penalties and interest, making you pay much more than you really owe if you are late?