Did I do the right thing...?

Here's the situation: my sister and brother in law got a 30 day notice to vacate because they were renting a condo and the owner decided to sell. My brother in law waited until the last minute to find an apartment. Finally, they found an apartment but they can't move in until September 15 (they have to vacate by August 15). They have two kids. Since they have to vacate and can't get the apartment for another month, they want to stay with us (we have two kids of our own). I absolutely refused because we rent an apartment and the landlord will get concerned with so many people at our place for a month. I love my sister but I need my sanity. I finally got their landlord's number and explained the situation to them and got an extension. When the landlord went to collect rent, my brother in law refused to give it and now says he doesn't have money for rent. Instead of staying there another month, and moving into the new apt. on Sept. 15, he insists on staying with us. Any ideas?