While Woofer and Whimper "talked" to each other (each with Southern accents), they only barked to the kids. (In "The Amazing Heist" they howled, leading to the discovery of a hidden ultrasonic signal in a recording, that helps to solve a mystery.)
Formally, members of the Clue Club have to be at least 14. Despite being a year shy of the qualifying age, Dotty's research and deductive prowess made her a valuable (if under-appreciated) asset to her elder brothers and elder sister.