Not to even think that I understand the Welsh language, this is Ty'n ddol isaf, which means 'lower meadow'. Makes sense, since Ty'n dool is just at the bottom of the hill from Pantgwyn. Both houses were occupied until the late 1700's, but Panygwyn eventually became a cow house. Ty'n ddol did end up being restored in the 1860's, so that Roy's Great Grandfather Griffith could move there after suffering from TB - he was living at another homestead called Hendre Bach.
The Watkins family would never lose either Ty'n ddol or Hendre Bach until 1937. Now Ty'n ddol has been purchased by an English couple, but I'm not sure what they are going to do with it.