Assuming you took a deposit towards the last two weeks of care then they are out one week. At the same time it rarely happens that a family can make the move at exactly the time given. When you give notice it is somewhat understood that you are required to give the full notice but if they leave before that there isn't much you can do because they have to take a space when it is available and not fair that they should have to pay twice for a space when they are the ones being asked to leave regardless of the reason.

Would you consider keeping the twins if they are putting the older in a centre if he was the issue.