I was wrong with "Back then you were already my wife." Since "even" wasn't one of the hints for "už," while "already" was, I think my translation should be acceptable. I will report it, but if I am clearly wrong, please let me know!
Multiple alternative translations are accepted, but there is nothing wrong with 'You were even then my wife." It would certainly be used much less often than other options, though, especially in the US.
Nope, this English translation doesn't make sense at all. I'm American though, Brits do you say this?
In this sentence, "even then" more or less means "at that particular time." For more, see, for example: https://www.merriam-webster.com/dictionary/even%20then. But there are close to 50 other accepted translations which you can use instead.