If they have your account's username/password (or stolen valid session cookie), they don't need need to be on your home network to access your cloud services like facebook/google drive. They can login to your accounts from their computers (pretending to be you) and for example delete files from your google drive. Then when your computers sync with google drive, the expected behavior is to delete those your hacked account deleted (as google thinks you decided to delete them). Change your passwords and force logout active connections.
For google you can go to their security checkup page at:
https://myaccount.google.com/security-checkup/
I would consider enabling two-factor authentication as well as reviewing all the existing devices that are currently logged in.
Similarly, I would check your facebook account at:
https://www.facebook.com/help/securitycheckup
If you think someone has installed malware on your computer, it may be necessary to backup relevant data and reinstall the OS from a trusted source.