I can't imagine the emotions your facing, the thoughts that must be running through your head. feel free to let them out in a reply to this if needed.

but first of all, could you give more context? do they know you know? if so, what were their reactions when you found out? did they both seem willing?

I suggest making sure your son wasn't raped, he may of been pressured into it or even forced. And the other way round of course.

Gather evidence that it happened if you can, get them to confess to it on a recording maybe. Then get Child Protection Services involved, your wife is clearly not a suitable parent to your son.

If Child Protection Services fail to separate them, then maybe even take it to the police if incest is illegal in your area.

And most of all, please get yourself therapy, as-well as your son. Give him the chance to reform himself, he's young, don't let this be the end of his reputation and future.

I'm sure you love them both dearly, but your son is your son and the one you're responsible for.

I'm sure you must feel sick to your stomach, and I'm truly sorry for what you're experiencing, please take care of yourself.