Elisabeth of Brandenburg, Duchess of Brzeg-Legnica and Cieszyn
Elisabeth of Hohenzollern( 1 May/ 29 September 1403 – 31 October 1449), was a German princess member of the House of Hohenzollern and by her two marriages Duchess of Brzeg- Legnica and Cieszyn.
She was the eldest daughter of Frederick I, Elector of Brandenburg by his wife Elisabeth, daughter of Frederick, Duke of Bavaria- Landshut.
Maria, Queen of Sicily
Maria( 2 July 1363 – 25 May 1401) was Queen of Sicily and Duchess of Athens and Neopatria from 1377 until her death.
John, Duke of Randazzo
John, Duke of Randazzo (1317–1348) was duke of Randazzo, Athens, and Neopatria, Count of Malta and regent of Sicily (1342–1348).
The fourth son of Frederick III of Sicily and Eleanor of Anjou, he was the most powerful nobleman in Sicily during the reigns of his brother Peter and his nephew Louis, during whose minority he was regent.
He kept the peace during regency, though he supported the Catalan party over the local Italian nobility.
Thus he appointed Blasco II de Alagona, a Catalan, as his successor.
War broke out upon his death during the Plague.
He married Cesarea, daughter of Peter Count of Castalnasetta and had three recorded children:
Frederick I who succeeded him as Duke of Athens and Neopatria; and two daughters Eleanor and Constance.
He died of the Black Plague in 1348 and was buried next to his father and nephew in the cathedral of Catania.
John II of Legnica
John II of Legnica( 1477 – 6 March 1495) was a Duke of Legnica since 1488 until his death( with his brothers as co-ruler).
He was the eldest son of Frederick I, Duke of Chojnów- Oława- Legnica- Brzeg- Lubin, by his wife Ludmila, daughter of George of Poděbrady, King of Bohemia.
Manfred, Duke of Athens
Manfred( 1306 – 9 November 1317)," infante" of Sicily, was the second son of Frederick III of Sicily and Eleanor of Anjou.
He was appointed Duke of Athens and Neopatria in 1312 by his father at the request of the knights of the Catalan Company then in control of Athens.
Manfred was only five when he was named duke.
His father sent Berenguer Estañol as his regent.
In 1316, Alfonso Fadrique, Manfred's elder( but illegitimate) brother, was appointed vicar general of Athens.
The young Duke never set foot in his realm, however, for he died in a fall from his horse before his twelfth birthday.
He died in Trapani and was buried in the Dominican church located there.
His younger brother William succeeded him as duke.
George I of Brieg
George I, Duke of Brieg( Brzeg)( 1481/83 – 30 May 1521), was a Duke of Legnica during 1488- 1505( with his brother as co-ruler) and of Brzeg( Brieg) since 1505 until his death.
He was the third and youngest son of Frederick I, Duke of Chojnów- Oława- Legnica- Brzeg- Lubin, by his wife Ludmila, daughter of George of Poděbrady, King of Bohemia.
Frederick I, Duke of Athens
Frederick I (died 11 July 1355) was the Duke of Athens and Neopatria from 1348 to his death, also the Count of Malta.
He succeeded his father John, Duke of Randazzo, in Greece after his father died of the Black Plague, but he too died of the same plague seven years later.
Frederick was an absentee lord throughout his reign, although his regent Blasco II of Alagona, urged him to visit his duchy in 1349.
Frederick appointed Ramón Bernardi as his vicar general there, but the latter was opposed by the baronage, who requested his removal from power just before the duke died.
Frederick died young and was buried in Sant'Agata in Palermo.
Chiara Zorzi
Chiara Zorzi or Giorgio, also Clara or Claire( died 1454), was duchess consort of Athens by marriage to Nerio II Acciaioli, Duke of Athens, and regent of Athens during the minority of her son Francesco I from 1451 until 1454.
Ludmilla of Bohemia
Ludmilla of Bohemia( died 14 August 1240) was a daughter of Frederick, Duke of Bohemia, and his wife, Elizabeth of Hungary.
Ludmilla was a member of the Přemyslid dynasty.
She was Duchess consort of Bavaria by her marriage to Louis I, Duke of Bavaria.
Chrysostomos II of Athens
Chrysostomos II( 1880–1968) was Archbishop of Athens and All Greece from 14 February 1962 to 11 May 1967.
His Beatitude Chrysostomos II( Hadjistavrou) of Athens was the Archbishop of Athens and All Greece and primate of the Church of Greece from 1962 to 1967.

Question: Who is Frederick I, Duke Of Athens's paternal grandfather?
Answer: Frederick III of Sicily