Need advice regarding family visiting

Sam💫 • Miscarried first pregnancy early March 2015 at 5.5 weeks. Expecting our rainbow baby Feb. 2016 ❤️
My brother, sister in law and nephew visit once a year from across the country. We are not super close but they usually stay with my parents when they are here. However, this year, my husband and I are buying that house from my parents 1 week before they come. We are uncomfortable with then staying with us for 2 reasons: 
1. We will still be unpacking and settling in. 
2. My SIL is bringing 2 of her other teenage/young adult sons that I don't really know. We work during the day and don't feel comfortable having them all stay there while we are not there. 
However - I told them things might be hectic with the move and they keep pushing to stay. Should I bring up the second point? I feel like they will get offended (i probably would too if I were them) - the problem is, there is really nowhere else for them to go. They don't have a lot of money and can't afford a hotel. 
I don't think that I am not wrong for feeling this way, I just don't know how to stay firm on this without seeming like a selfish bitch or not a "good sister" - please help!!!!