Ok... flying blind here.
My teens say that all they want to do this summer is hang out with their cousins on a lake where their uncle can drive them around on a boat.
My mother-in-law suggested Michigan. Ok.. I'm game. I've never been to Michigan, I know nothing about the state and I don't even know where to start looking.
Good sized lake or Lake Michigan. Dock. Ability to rent boats. Housing for up to 25 people (this can be multiple homes in a general area).
What is the best of Michigan? Give me some suggestions that will show off your state!