All of mine and my exes devices were under my account. My ex husband just changed the email and password to that account. How do I get all the devices I have onto my new account?
You want to do a Factory Reset (towards the bottom of the page - not just the simple reset/reboot.)
After the https://support.roku.com/article/208757008 is done for each Roku device, create a new Roku account of your own, and use that account on your Roku devices.