Even a factory reset won't work, unless you remember your Google account login and password.
In the future, instead of relying on your memory of a few passwords for everything (if a site gets hacked and they get your login and password, they get your login and password to all the sites you used the same one on), use a password manager that can keep its data file in the cloud. (A lot of people here like
LastPass Password Manager. [I've been using
Keepass2Android Password Safe with the data file in the cloud for so long that I keep it.]) That way you only have to remember one password, the one to the password manager. And you can use a different 50 or 60 random character password for every site, every app. That way, if someone gets one, they only get one. And if you keep the password to your tablet on it, and keep a copy on another device (a phone, a PC, a laptop - or all of them), if you're locked out of your tablet, you just look up the password in some other device.