First of all, you need to confirm that you are an authorized user, NOT a joint user.
Joint users have equal responsibility for the account, no matter what the other person does.
An authorized user is just that, someone with no ownership of the account, but is authorized to use the CC. AU's are not responsible if the account goes sour. If that happened, you would need to get yourself removed from it as soon as possible, and make sure that it stoppped reporting.
Sometimes, the AU account continues to display, which can be good or bad. I took myself off DXH's Discover card in January, with its lovely, long history, yet it's still showing on my reports. Yay! On the other hand, I briefly had DXH and DD#1 on my American Express Gold card when they traveled, and then I removed them again. The card is still displaying on both their accounts, nearly two years later, lowering their AAoA (average age of accounts.)
At any rate, it sounds as if your card is an AU card, which is good. You can choose to stay on it or not, just so you realize that there can be a delay in getting it removed from your reports. It's hard to say from what you wrote if the card is helping or hurting. There might be another reason that TU is lower.
Do you have any credit in your own name? If not, you need to open one or two cards before the AU card vanishes from your reports. It's easier to get credit if you already have credit.
When you look at your two score reports, what does screen two (with the positives and negatives) say are your negative factors, in order?
And by the way, if I haven't confused you enough 
, I had to move your other post over to Rebuilding Your Credit. Look for the placeholder here on the Divorce board with the name of your post, and you can click on the link to take you over there.