I would also contact the family and at least offer them the option of starting early. It's not always possible and money can be a factor (I'm sure you all remember well how lean things can get when you're on mat leave and there is only 1 income coming in) I would be inclined to save the space for them too but I would also firm up their commitment to you. You don't want to be caught saving a space and have them back out. I'd probably also advertise, cover all of my bases.