Even though your In-laws are well into their 60's, they still love sex and they can't stop fucking. They've been staying with you for two days now and you and your wife can't get a wink of sleep with that bed rocking back and forth all night long and the two of them screaming at each other, "Come on hit me. Yes. Now shove that thing in my hole. No the thing in your hand. Yes, the wooden thing. Get it in there. Hurry for God's sake hurry. Not so loud, you might wake up the kids."
You and your wife may be "the kids," but they're still the guests in the house. Tell them to keep it down tonight. Say, "Look I know you don't have long. God knows either of you could go any minute. In the blink of an eye. Just like that. So I don't want to tell you not to get everything you can out of your last hours together. I just want to ask you not to scream so loud when you come. And maybe don't throw the alarm clock at each other. That thing really makes a racket when it slams against the wall. Additionally, Howard, when you bellow at the ceiling it makes the dog think there's a predator in the house and we have to put him out in the garage. Finally, there's semen on the windows and I didn't put it there. That's in-law semen. Clean it up."
Your wife will sulk when you go back to your room. They never talked about sex in her family. The kids were just forced to listen to it and pretend nothing was happening. She was 100% against you going in there and telling them to quiet down.
"How am I going to face them at breakfast now that they know I know what they're doing?" she'll ask.
"You have no idea what they're doing," tell her.
"What do you mean?" she'll ask. "What are they doing?"
Don't tell her what you saw. Don't tell her that the guy who stands out front of the liquor store is upstairs with her parents in their bedroom. She doesn't need to know.
"Just trust me," tell her. "You can enjoy your breakfast just like any other morning because you haven't the slightest clue what might be going on up there."
Then just roll over on your side, clench your eyes shut tight and shiver yourself to sleep.
Happy In-Law Sex Day!