The only way to switch them back is to have sex with one of them until you both orgasm.
They have to be lucid and awake. You have to be lucid and sober. Everyone will remember the experiences after they switch back. If they remain in the switched bodies for one week they both die a painful death.
Are you fucking your Significant other in your parents body, or your parent in your significant others body?
This is a famous one.
See, this one isn’t difficult.
Any WYR with a sufficiently brutal group ends up with someone having to bang a parent.
I’ve had this one before, and it falls under the general solution of doing the thing that makes the condition successful. As I would not be able to maintain an erection with my mom’s body, the only successful option is to bang her in my wife’s body (sorry, we’re monogamous, so no gf).
And, frankly, that’s the best solution anyway. Anyone’s mom is going to be older than them, even with adoption. So the mom’s body has a higher chance of having something that interferes with sex and/or orgasm. Post menopause, that’s an even higher chance. So the person in that body is possibly going to not only take longer to fulfill the requirements, but it may even be painful to do, or impossible.
Of course, there’s also the “neither” option where you tell them you don’t care and walk away into the sunset, but that violates the spirit of WYR participation imo.
Also, my mom is a fairly rational person most of the time. So it wouldn’t take a long time for her to reach the same conclusion. The real barrier would be deciding between me and my wife if it counts as cheating ;)