<human>: Can you summarize the given text in a few sentences?

My family and I were on vacation for three weeks in Europe and when we came back we found a case of budlight, some cups, and beer pong balls in the BBQ. My first inclination is to think it was some friends my little sister told we were going out of town and could use our place for parties. 

My parents had a friend that came just after we left to check on the place and she said she saw two cases of budlight next to our patio but thought nothing of it. So these people obviously knew exactly when we were leaving. Our friend also said she saw christmas lights and things like that hanging up another day she came by. I really don't know why she wouldn't have called the cops at this point, but it is too late for that. 

We also had a key to the back gate very well hidden so the gardeners could come in. I'm pretty sure whoever came in had to know where the key was because it was pretty well hidden and I doubt they would have jumped the gate. It is 6 feet tall with some nice spikes on top, so not to fun to be doing that every night.

I would really love to catch these people, but I'm not really sure what I can do. I am 100% positive it was my sister simply because she is the nosiest person in the world. She always wants to know who is doing what and loves to discuss the possibilities. A month ago, she was obsessed with finding out who these people were that doorbell ditched us to the point where she wanted a family friend to look up the plate info. Now, when someone comes into our backyard and throws a party for three weeks, she seems as if she couldn't care less, so I figure it means she already knows who it was. So any tips on how to get info out of her are welcome as well.
<bot>: Vacationed for three weeks, people threw party in our backyard. It was probably one of my little sister's friends.