Clearfork,
That would really depend upon, would one of the adults want to share a bed with one of the children. The beds for the children are really just big enough for 1 child, unless both children are very small. Small, like less than 2 feet tall and slim.
However you could put the two largest children, who must be less than 4 feet tall, into the two childbeds. Then share the lower adult berth with the smallest child and one adult, while the other adult occupies the upper adult berth.
If you choose not to do that, I can't imagine that the car attendant would not allow you to have all five people in the room during the day. There really is no reason that anyone should stop you from doing that. Mind you that the person riding in coach, would need to be escorted by one of those riding in the sleeper. Also be sure to carry the sleeper ticket stub with you.
Finally, you could consider getting a standard room for the 5th person. Ask for a room on the lower level, so that they can be close to the family room.
