That is scary! The same thing happened to my grandma, who lives alone. Her neighborhood has started to become rough in the past few years. A teenage girl desperately needed to use the phone, so my grandma let her in. A bunch of her friends followed her in and were going through the house, up in her bedroom and everything!
I don't think they took anything that time but were checking out to see what she had. Things have been stolen from her yard, and her shed was broken into and things were stolen from that too (like a snowblower that was stolen in July!) Her half-brother now lives in her basement suite so that gives us a little more piece of mind that she's okay there. But she has said a million times, she loves her house and when she and my grandpa moved in, she said it would take wild horses to drag her out, and she still feels that way.
I hope you can convince your aunt and uncle to be careful!