Does anyone know how to get rid of bed bugs

My grandparents have bed bugs. This is the first time they’ve ever had them. I’ve never had them so I’m not sure what to do to get rid of them. They’ve had an exterminator to come out twice and it didn’t work. They are using the powder and cleaning their stuff but that’s not working either. We are getting frustrated now and need other options. If you’ve ever had them what helped get rid of them? Thank you in advance mamas