Good question.
If Astarion was a gnome, I wouldn't hate him so much.
Karlach would easily work as a Dwarf.
those 2 are perfect as the races they're, Gale however would fit better as a gnome, specifically a rock gnome, they guy is annoying and has a know-it-all personality would be in character for a gnome, plus there's his drug addiction, Gale is that coke your snorting, no it's "MAGICAL ARTIFACTS".