If you cannot find reservations for 5, try looking for a party of 6. The reservation system has a harder time with odd numbered parties because most parties of 5 will be seated at a 6 top and the system wants to fill every seat at the table. When you arrive at the restaurant just let the castmembers know there are 5 of you. You will not be charged for the "missing" person. Be sure to include everyone in your group when looking for reservations because of fire code regulations, so don't try looking for 4 because then one person in your group might not be seated.
You could also look for 2 separate reservations as close in time as possible and when you check in ask to be seated together, but it is only a request and while castmembers will do their best, there is the possibility you will be at 2 separate tables on opposite sides of the room so this would be a less desireable option for our family.
If this is for the vacation that is starting in 10 days, there are cancellations at the last minute because most don't want to pay the $10 per person penalty so keep checking even after you arrive at DW.