Upper bunks require some agility to get into. I usually suggest that the smaller individuals use the uppers. The lower bunks are also wider than the uppers.
The Family bedroom has one set of adult sized bunk beds and one set of youth sized beds (slightly shorter than the adult beds). Since you say only one adult and one child in your family are "larger" you should be fine with the two lower bunks.
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Trust God, love your neighbor, and never mistake opinion for truth.
-Mr. Toy
The Del Monte Club Car