My simple rule on loaning: While it is in your possession, you break it, you replace it with new. Simple. We know there are lots of systems (with a learning curve) and this simple rule applies to every nut and bolt. This rule also extends to all risks, even what is entirely out of their control. Whatever is loaned is returned whole or the borrower makes right. If they are in a financial position to replace any/all, proceed to point #2.
2). Do they have their own truck properly equipped to tow your rig? If so, do they have towing experience? If they are expecting to borrow your truck as well, they likely do not have towing experience and, by agreeing, you are putting all of them at risk of great peril. Keep in mind, all of the above has you (and your wife) on the insurance hook for anything they might do... to equipment as well as liability to others.
If they are financially capable and have at least some towing experience, you're probably going to give in and let the wife loan the rig. Happy wife, happy life.