See if you can boot to Safe mode and deactivate those Device Admins. As long as they are Admins, you can't uninstall the apps... if there's an uninstall in the first place. Also, download
Malwarebytes from the playstore if don't mind risking a sign in. Or you can download it from APKPure...
Malwarebytes... and sideload it. Whichever way you get it, update Malwarebytes and have it scan your phone. Have it fix whatever it finds. See if you can run Malwarebytes in Safe mode.
Also download and install
Avira from playstore or APKPure..
Avira. Update and have it scan the device and fix whatever it finds. Also see if it'll scan in Safe mode.
You can check to see if the tablet is actually rooted by downloading
Rootchecker from the playstore, or again from APKPure...
Rootchecker.
To sideload apps, in case you don't know, just means to install a downloaded app from a flash drive. You will need to be able to connect the flash drive to your device with an OTG cable, or if you have a flash drive or card reader that connects straight to the device connector, you can use that.
Eventually, we want to be able to factory reset the device and totally wipe it.
I totally understand your anguish and frustration. I've been working on PC's for years and a lot of that time was getting rid of malware and virus' on friend's and family's computers.