This is from the T-Mobile Support website at This link
Samsung Galaxy Tab E
Master reset with hardware keys
A master reset restores the original factory settings and may delete your personal data on the internal storage, such as downloads, ringtones, images, apps, contacts, and Visual Voicemail. It does not delete data stored on the SIM card or SD card.
If the device menus are frozen or unresponsive, you can master reset using hardware keys.
Turn off the device.
- Press and hold the Volume Up key and the Home key, then press and hold the Power key.
- When the Samsung Galaxy Tab E logo screen displays, release only the Power key
- When the Android logo displays, release all keys ('Installing system update' will show for about 30 - 60 seconds before showing the Android system recovery menu options).
- Press the Volume Down key several times key to highlight 'wipe data / factory reset.'
- Press Power button to select.
- Press the Volume down key until 'Yes -- delete all user data' is highlighted.
- Press Power button to select and start the master reset.
- When the master reset is complete, 'Reboot system now' is highlighted.
- Press the Power key to restart the device.
If you no longer have access to granddaddy’s google account, you may have to start one of your own :)