The fact that such a question had to be asked to a newspaper column suggests that we are already dealing with a less than harmonious situation.  A will that assigns equal rights to the cottage is no different than saying divide my estate into equal portions.  There is no obligation to assume and maintain ownership of an asset that can be sold or otherwise transferred in exchange for other assets.

I suspect the issue is that the perceived value of the cottage is the problem.  Everyone loves the idea of the cottage but no one thinks the repairs and maintenance is should cost as much as it does.  Similarly spending time at the cottage is priceless, but paying for your share of the cottage commands a significantly lower valuation.

Of course it could also be a case of believing that the one sibling doesn't want to "own" the cottage but fully expects to continue spending those weeks there every summer.

One more reason why rentals make a lot more sense.