No way is your tongue weight 690. Your stated dry weight multiplied by 13% is 860. If your going to calculate tongue weight, use the TT's gross weight. And I'm sorry, but upgrading to better shocks and air bags does not increase payload - it's like putting a band aid on a broken leg.
Hopefully you understand all the weights that subtract from payload.
I don't know about ratings for an excursion, but most likely won't cut it, unless you can find it in a one ton version. For a big family such as yours, the advice on the van is a great option.
Here is a link to the CAT Scale locator is your inclined to find out actual weights.
Good luck.