Complex sentence: Nest is the female progenitor of the Fitzgerald Dynasty, and through her the Fitzgeralds are related to Welsh royalty and to the Tudors (Tewdwrs), their cousins, who are likewise descended from Nest's father Rhys ap Tewdwr (Anglicized to "Tudor").
Split into simpler sentences: Nest is the female progenitor of the Fitzgerald Dynasty, and through her the Fitzgeralds are related to Welsh royalty and to the Tudors (Tewdwrs). The Tudors are descended from Nest's father Rhys ap Tewdwr (Anglicized to "Tudor").