Unfortunately if you can't remember your email you will just have to reset the cameras, (which will cause you to lose all video history), and set them up with an email you remember. You can also try to see if there are any other accounts you used the forgotten email with in case you can find it that way.
Thanks for lending a hand, @MetalGlacier.
@Bmcockerill, you will need to factory reset your Nest cameras and set it up again using your new phone and an email address you have access to. Take note that your settings and entire video history will be removed in the process. Let me know if you have any other questions or concerns.
Just checking in to make sure that you've seen our responses. Please let me know if you have other questions or concerns as I will be locking this in 24 hours if I won't hear back from you again. Feel free to start a new thread and we'll be happy to help.