Different Upgrade Dates

Yes. AT&T does their upgrade eligibility on a line by line basis. Since one of the determining factors is how much is spent per line you end up with situations like yours.

For example, from the data you've given me I can make an educated guess that your wife's line is the primary on the account. What that means is this: lets say you have the family plan with the base price of $69.99, then the primary line has a voice plan costing $60, and the second line has a voice plan costing $9.99 (and any additional lines are also going to be $9.99). Add on to that the $30 data plan and you will see that:
Primary = $60 + $30 + messaging > Secondary = $9.99 + $30 + messaging, thus giving the primary line an earlier upgrade date.

 

My wife and i have the same issue. My line is eligible on 7/12 and hers has to wait until 1/20.

Very annoying as it's almost impossible for a second line on a family plan to hit the $99 mark.