Stuttering is not incompatible with high verbal intelligence. The former is a speech impediment, while the latter is a language gift. Just because his oral-motor skills for speech were weaker, does not mean his cognitive language abilities were also weak.
The balanced profile is not notably less typical than an unbalanced (high GAI/low CPI) profile, in GT profiles. So both your DS and your DD have profiles that are reasonable for very high ability individuals.
Similarities is a measure of abstract verbal reasoning/verbal concept formation. Although responses are purely verbal, it requires very little expressive language, which allows for nonverbose individuals to perform without penalty. It is also untimed, which reduces some of the stress that stutterers feel under time constraints.
Your DD's FSIQ is actually lower also because VCI and VSI are reversed, and VCI is weighted twice as much into the FSIQ as VSI is.
