You seem to be earnestly looking for advice, but whenever it's offered, you always come back with why it won't work, or why it can't be done. Mark's (and my) advice may or may not work, but why don't you try some things, and see what works and what doesn't?
As for your convos with her when she drops your son off: waywards desperately want to NORMALIZE their illicit relationships. They want family members to accept their OM/OW, they want everyone to treat them the same, etc. Don't play the game. Be civil, be polite, but cut the convos down to about 5 minutes.
