You might need to retain an attorney

The key point of your case is to persuade the IO that the conviction is not a crime involving moral turpitude (CIMT). Unfortunately, DV is a typical CIMT by consideration of USCIS. Now the conviction has been a done deal, you can change that, not even with expunge or executive pardons, you need to show USCIS 2 things:
1. give them any extenuating circumstances for the crime, so they can have some space to work---if the IO is nice, understanding and willing to give you guys a break. Without that, any IO cannot do anything, did they ask for any statement from you? What they could be looking for is your guys' explanation for what happened for the DV.
2. you may have to retain a attorney, majorly to show USCIS your determination that if they deny your case, you guys are willing and capable to hire a lawyer to fight to the end.
Although the IO approves your case, a complicated case like yours will go thru many levels of internal checks and approvals, so it is gonna be long. Don't ever give up. Thanks.