There are mtDNA identified errors in Family 5 which show that the family actually descends from three separate founder mares - see The Massey Mare entry

Grandam of Grey Skim (taproot mare Family 5-b) and 3rd dam of Castanea (taproot mare Family 5-d) and Belvoirina (taproot mare Family 5-e)

In addition to her descendants via the above horses and her five generation progeny below, the best horses which descend from Young Hag include Jack Spigot (1821 St Leger), Deception (1839 Oaks), The Merry Monarch (1845 Derby), Finlande (1861 Prix de Diane), Saint Cyr (1875 Poule d'Essai des Poulains), Fontainebleau (1877 Poule d'Essai des Poulains),

Jack Hare Jr. (1918 Preakness), Astec (1967 Prix du Jockey Club), Pleasant Colony (1981 Kentucky Derby, Preakness) and many other classic winners

Grandam of Platina (1795 Oaks); 3rd dam of Election (1807 Derby, Champion Sire 1825); 4th dam of Neva (1817 1000 Guineas, Oaks); of Matilda (1827 St Leger); 5th dam of Moses (1822 Derby); and of Frederick (1829 Derby)