It's a lot to read through and I don't always explain things as well as if I could talk to you. If you were to switch to a 10 gig shared data plan called mobile share value the it would be $100.00 for the data + $15 per phone for a total of $145 before taxes and fees. You can get 15 gigs for $130 plus $15 per phone for a total of $175. Bumping up to 20 gigs would cost $150 plus $15 per phone for a total of $195.
And the mobile share value or regular mobile share plans come with unlimited talk and text.
Here's a link to the page explaining the cost:
http://www.att.com/shop/wireless/data-plans.html