"My little granddaughter, Emilie, cared for [the horses] and came to love them like her own family." (21.13)
Emilie's grandpapa has no heirs after Emilie's death. Yep, he's the last of his bloodline. That's probably why he goes to such great lengths to find Joey and Topthorn and essentially adopt them. With the horses back in the family, Emilie's family memories can live on.