Can't remove device from Fathers account

[SStahl]

My Father passed away in late November and we've been selling his estate to pay for the funeral cost and other expenses. Anyway that doesnt really matter.

My dad had an Arlo Q and two other Cameras (they are pretty beat up) that we are trying to sell. My issue is when we sold the Arlo Q I wasn't aware that they had to be removed from my Fathers account. I was contacted by the buyer and he asked me to remove it. My dad does not have the Arlo app on his phone and when I try his email (that I know of) it doesnt say he has an account. He obviously had an account but im not sure what his email was. Im not even sure what his password would be to this said email.

Is there a way to remove the device from his account without knowing his login information? I have the camera/serial number. 

Kinda lost on what to do, thanks