I can only imagine how tough this must be for their parents. Handing over that kind of control and financial independence has to be really scary, especially after a lifetime of being so careful with their money.
But it's so great that they're being proactive about it and getting your wife and her sister involved. Even though it's a big change, at least they'll have the support of their children to help them through it.
I am pretty sure your wife will do well with her inheritance because you will be there every step of the way to guide her.
Yeah - I think that they are a pretty decent family all in all, so there shouldn't be too many issues.
I would spend it all on candy ;)