Personally I would just go with Florida. Trying to force them to go out of their comfort zone might be done with good intentions, but risks resentment in addition to not feeling appreciated. You take them some where you mother in law doesn't want to go and you may find yourself worse off than if you didn't take them any where.
Mother in law seems to be on board with the USVI now. This will probably be what we do. Not sure what made her turn the corner, to be honest. Of all a sudden, she wanted to go there. She randomly texted a B&. We've never been, but have wanted to go.
