How to factory reset when a tablet will not restart? More explanation below

I'm hoping someone can help with this issue. Essentially, we are locked out of the tablet and unable to factory reset or reboot it into recovery mode The tablet in question is a Samsung Galaxy A8 tablet that belonged to a deceased relative. The tablet has started asking for a password, but we've never set one. I assume it's the password for the google account on the tablet but we don't know what the password is, and the owner of the tablet doesn't even know which email address is associated with the tablet so we can't reset the google password. We are unable to restart the tablet to factory reset -- when we try to restart it it just asks for the password again and won't even reboot. Pressing and holding the power button to force it to shut down is also not working. The tablet is also in safe mode, not sure why this is but we can't make it exit safe mode. I believe all the volume buttons are working as they should. I thought about using ADB but I don't believe USB debugging is enabled, as the owners are not great with technology and probably won't have looked at the developer options. The only potential solution I can think of is letting the battery run all the way down and then trying to boot it straight into recovery mode, but that will take a very long time. I'd try to remove the battery but the tablet isn't in my possession (I'm helping relatives remotely) and I don't trust the owners not to mess that up! So, is there a way to make the tablet able to restart normally so we can enter recovery mode, or alternatively to turn USB debugging on remotely so I can use ADB? TIA (and sorry for the very wordy question!!)