According to the Catholic Church, what is to become of a family when the married couple discovers they are brother and sister? The scenario

A brother and sister are separated at birth and grow up not knowing of each other. Years later they meet and unbeknownst that they are brother and sister, fall in love, marry, and have children.

The question

Later, perhaps due to a search in family medical history, they discover this fact in their past.

According to the Catholic Church, what is to become of a family upon this discovery?

An answer may include a real life example.
Legally in most places a marriage that would have been illegal if the facts were known is automatically anulled - in other words it is deemed never to have taken place. Here is a page about it from Californian law..

Wikipedia gives grounds for automatic annullment of a marriage according to the Catholic church - it includes 'consanguinity', i.e. close affiliation by blood. Siblings would certainly count.

The anullment of a marriage does not affect the status of the children. They are considered 'legitimate' as long as at least one parent entered into the marriage in good faith. The anullment does not take away any of the duties of the parents to care for the children.