That's just crazy.
I also never aspire to own a vacation property. WIth taxes, maintenance and all the pain in the ass of renting/property management, I feel I'm much better off just renting a property for the times I decide I want a vacation. Even if it's an extravagant expense for a week, it's a one-time expense with no further obligation.
The people I know who have cottages, it seems almost like a burden - like you are obligated to spend all your spare time there, spending time schlepping back and forth, keeping it up, opening it, closing it, cleaning it. Meh. I'd rather show up, live a life of leisure for a week and then go home. :)
Your Sister and BIL must be crazy wealthy to be able to drop that kind of coin on a vacation property.