[McGary911]

I think the actetone would work on the hard surfaces but test, test test.

You plan on doing this yourself or hiring a professional service? There's a ton more surface area in an RV than an M2.

Here's an idea. I'm sure a few of those permanent highlighters are still around (even if they're used up). Get in touch with the manufacturer and let them know about your situation. I'm sure they could recommend the mildest product for various surfaces that would still do the job. They might even have some stuff in house that they can share with you. It's worth asking.

Tough family situation. It sounds like your inlaws did the best they could.