Of course, this being the wishing stone, and the fact that Jon's wish was so vague, the outcome wasn't going to be so straight forward.
For the Gibsons, the father (James) and the mother (Linda) would stay as father and mother, respectively. But not only would Jon and Mikey become female versions of themselves, they (along with Zoe) would also all become the same age, averaging out at 14 years old, as triplet sisters.
The Fergusons, Blacks, and Meshidas would all be straight forward, meaning that the father would remain the father, the mother would remain the mother, and the daughter would remain the daughter. But with the Meadows family ... while Biff and his younger brother Wesley would become female versions of themselves, they would remain their own ages. And their father Gary would turn into their new mother, and their mother Loraine would turn into their new father.