Hello there, bigheadmonkey,
It sounds like you're having some trouble logging into your Google account while on Safari. Just to make sure were clear, when you try to log into Google, is it that you're seeing your old account email address instead of your current one?
If so, then do you have your Google account saved in either Keychain Access or in iCloud Keychain? If so, then it's possible that it has your old credentials saved, which is why they appear when you try to sign in.
To check Keychain Access, open Keychain Access by searching for it using Spotlight.
Then use the search bar in the window and search for "Google". Select the account that has the incorrect credentials and delete it by holding down the Control key and clicking on it. Then select "Delete".
Here's more info on Keychain Access.
If you can't locate the old account that way, then it may be saved in iCloud Keychain. Use the steps under the section "How to find passwords stored in iCloud Keychain" to check and remove the account.
Let us know if that helps, and have a great rest of your night!