My best friend married my husbands best friend shes having an affair please help?

So my best friends having an affair with my son,so my don is also cheating on his wife but I think he's being paid so technically its his job. So what do I do?! If I tell then I could lose my friendship and my daughter in law plus my son would be out of work and would have to live with us again. But if I don't tell my husband would be pissed. He spends so much time with john *the gut being cheated on* they havesleepovers, go to the sauna,they also go on mini vacations alone to nudist beaches. So yeah what do I do?