Mirabelle Hubble is Mildred Hubble's last magical ancestor. ... Mirabelle re-ignited the Founding Stone, but to do so she had to give up not only her own magic, but that of her descendants for twelve generations- Mildred is the thirteenth generation, making her the first magical Hubble for centuries.

Is Izzy's dad Mildred's dad?

Dave "Spike" Jones is Mildred's and Izzy's father, and Julie Hubble's former boyfriend.

Who stole the founding stone?

In The Friendship Trap, the Founding Stone goes on display in the school hall, however Beatrice Bunch and Sybil Hallow accidently take the stone when Beatrice's sneezing teleports her and Sybil around the school.