You can always say "I prefer not to talk about this anymore." if they refuse to drop it. Most of the time people refuse to see what they don't want to see, because if we acknowledge it's a problem them we are actively choosing not to fix it. Whatever your in-laws want out of this situation is probably impossible, so they stay stuck. Even though it's a choice, they probably won't "hear" it when you try to tell them. That's their choice too. You have the choice to listen as much or as little as you want. I hope it helps!!