I've done the trade in for three games this year. The only way to ensure you have seats together is to upgrade your own seats. So if you have seats in the level 5 category you have to move to level 4 or better. They should allow you to stay at your same price level as your current seats.
The other thing I learned was that you have your "4 trades" but if you trade a game and upgrade your tickets so you can have your seats together that counts as 2 trade-ins which is complete BS. After trading in my third game I told my trip that I planned on doing the last trade and she told me I wasn't able to.
That is shady. I would have blown a gasket. They absolutely should have told you that before you upgraded.