If the whole extended family, including S16, knows, then why would anyone think S12 doesn't? You & your W need to manage the message, but only because the ship has already sailed and your credibility with your sons is at risk.
Forgive me if I'm misremembering, but wasn't S12 in the car with you when you discovered the most recent A? If so, how did you deal with that?
Me42, H40 D12, S8, S7 A revealed: 7/13 Sep 4/14; Agreed to D 1/15