The only moderate regular hotel room that can sleep 5 is Port Orleans Riverside (they have a trundle bed). I don't know how big your adult children are, but that might not work. Also, you are going to be charged an extra $15 a piece at a moderate for having more than two adults in a room. That will add $45 to your room rate.
Have you thought about renting points from a DVC member for a two bedroom? If you rent Sunday through Thursday the points are cheaper (Friday and Saturday points are usually double). You could get a 2 bedroom at OKW in value season for 22 points a night. At $9 or $10 a point that's $198 to $220 a night - but you'd have about 1500 square feet of room, not to mention a full kitchen, living room, two bathrooms, washer and dryer, and jacuzzi tub.
Or, you could get two rooms at a value. If Disney offered you a code or you could get an AP rate I'd try for 2 rooms at a moderate. Of course, you'd still have one extra charge for the additional adult, but that's better than three additional charges and 5 adults crammed in one small room.