That seems to be interference with nearby wireless networks or electronics. Also, depending on how far your laptop is from their wireless router.
Next time that you stop by at your parents home, ask their permission first if they will let you do a minor change in their router settings, if they won't let you, perhaps another option is a wired connection.
On your next visit, please Install and run Xirrus Wi-Fi Inspector
Click on the 'Show Networks' to display all wireless networks on the xirrus icon on your desktop of if you have one running in a corner. Tap the Printscreen key on your keyboard, open up Paint then choose Edit from the Menu and select Paste, then SAVE it. Upload and attached it here, click on Go Advanced and locate Manage Attachments Tab and attached the file.