Short answers, pulled from the story.
Magnates of Poland and Lithuania were wealthy nobles who accumulated vast estates known as latifundia across eastern territories. Some families traced their ancestry back to Gediminas, a Grand Duke of Lithuania who ruled from 1316.
Powerful noble families won the struggle for political dominance in the Commonwealth during the second half of the 17th century. The Radziwiłł family led rebellions during The Deluge period while Sapieha families sparked civil wars in Lithuania around 1700.
Prominent lineages included Potocki, Zamoyski, Koniecpolski, Ossoliński, Ostrogski, Tarnowski, Kalinowski, Krasiński, Mielżyński, Branicki, and Zasławski families. Lithuanian noble houses included the Radziwiłł, Sapieha, Pac, Olelkovich, Goštautai, Astikai, Alšėniškis, Kęsgaila, Manvydas, and Tyszkiewicz families.
Major residences appeared as dwórs or dvaras structures and outright palaces across locations like Nesvizh, Slutsk, Biržai, and Białystok. Residences included Pawłowice, Iwno, Kėdainiai, Sieraków, Leszno, Rydzyna, Gołuchów, Jabłonna, Nieborów, and many others stretching from Ukraine to Poland proper.
The Third Partition of Poland in 1795 ended the Commonwealth's independent existence and began the decline of magnate power. Communist-ruled People's Republic of Poland eventually brought these aristocratic families to complete end after the Second World War.