The dry tongue weight at 925 pounds is more than your receiver is rated. Loaded, it will only go up. For a large family, I estimate the TT will be at 8500 pounds with about 1000 pounds of tongue weight. That is far too much for your Expedition.
You need to look at two different limits for estimating how much RV you can tow, not tow rating. Open the driver's door and look for this sticker on the door or door jam.
Subtract your estimated weight of family and stuff you think will be inside the Expy.
Then look at your receiver for something like this sticker:
Take the lower of the two and multiply by 7.7 for an estimated loaded TT weight.
My guess is you need to stick to TTs under 6k dry with under 650 pounds of dry TW.
