We spent a few days with my DP's family in a town approximately 5 hours by car from where we live. Meanwhile his brother wanted to take his two teenage girls on vacation at our place until Monday. We arrived back home today (Saturday). I told my DP they can stay till Sunday, as I have to go to work Monday, and need a little quiet down-time before then. I love family-time, but I really need some me-time, or I get exhausted and stressed out. DP knows this, and accepted. We also have a 10 months old son, who doesn't quite sleep through the night, to take care of.
There had been a miscommunication, though, and DPs brother thought they could stay till Monday and planned on this. He is now talking about cutting their trip short by a day and driving home tomorrow. He seems fine with this, though his teenage girls definitely do not. They want to stay.
YABU - let them stay, it's just one night, you'll be fine
YANBU - you said till Sunday, and needing some space and quiet time in your own house before getting up and going to work is reasonable
Genuinely asking, as I still have time to change my original answer. My DP would like them to stay till Monday, but he will respect my wishes, as will his brother.