Sal's grandparents on her mom's side are the polar opposite of Gram and Gramps Hiddle. Although we never officially meet them in this story, we get a few scooplets. They are very strict and proper, and they are always worried about being "respectable." Interestingly, this is the same word that Mrs. Winterbottom uses when she comes back home, explaining why she never told her family about her son, Mike.
We get the feeling that Sal's mom is worried that she is too much like them. Chanhassen Hiddle would much rather be like the Hiddles: spontaneous, fun-loving, quirky, and good.