Unable to remove email alias from iMessage

All these numbers can be removed by logging into

https://appleid.apple.com/

1. Go to Settings > [your name] > Name, Phone Numbers, Email.
2. Next to Reachable At, tap Edit, then delete your current Apple ID.
3. Tap Continue. Enter the Apple ID that you want to use.
4. Tap Next.

To remove some numbers (You need to sign out of FaceTime and iMessage)

Others you click on "x" to remove.