Fashion in the 1870’s was in a state of flux. (Isn’t fashion always changing?) Skirts were narrowing and the fabric was moving to the back of the skirt instead of the sides.
A fashionable lady–like Leonora or Aunt Emily–would be up on the most current styles, and dress accordingly.
Jo and Fred would not. They are not up on the current styles. They go for comfort. Jo is not one for stays. Fred is much more practical too. They are more likely to be found in a simple bodice and skirt.
Alistair is seldom dressed for the board room either–though, as a professor, he is sure to wear a jacket and tie in classes. In the warehouse, he’s in shirt-sleeves and a lab coat.
Kevin is much more likely to be in a suit, as he is in a professional position. As a detective, he would not be in a uniform, but Sergeant Doyle would be.