I had multiple DUIs that happened 12 years ago all within the same
time period. I am going to an interview where the job requires a
background check. It is for an estate attorney's office.
Even if I'm not asked, do I disclose this information during the
interview, being that it will probably be the only chance I have to
defend my past?
Since you already know there will be a background check, and since many background checks would discover multiple DUIs, I think it makes more sense to be up front about it than to let the hiring company be surprised.
This would be particularly so for a law office.
If you get to the offer stage and are ready to sign consent for the background check, just start with "I want to mention something that might show up on the background check...". Talk about what happened. Explain why it won't happen again. Finish with "I always believe it's best to be very honest."
When I'm hiring, I'd much rather the candidate be honest in the beginning than to try and "sneak one by me". I'm sure we can all remember how we felt when someone grudgingly admitted an issue only after being confronted with the evidence.
This won't guarantee that you'll get the job, but in my experience you'll have a better chance (particularly in a law office) by being completely open and honest.