It's not too far. I've done this same thing a couple of times.
One thing to remember though is the drinks at Animal Kingdom do not have tops on them. So, you'll have to navigate through the crowds with open drinks and food. It would probably be easier to get the kids' meals since they come in a box and your husband's burger first, let them get a table at the Flame Tree and you stand in line to order your meal at the Flame Tree.
It may also be easier for your husand to have you order his drink at the Flame Tree so he won't have to carry his burger and his drink.
Another thing I did was save one of our bags from when we made a purchase the day before, rolled it up and carried it in our backpack. When I got my son's meal at Restaurantosaurus, I put the food down in the bag and just carried the drink.
Hope this helps, Lisa