Complex sentence: Stefan Giller (1833 in Opatowek, Congress Poland, Russian Empire-1918) his elder brother Agaton Giller were two brothers who played an active role in the Polish independence movement and the Greater Poland Uprising.
Split into simpler sentences: Stefan Giller (1833-1918) was born in Opatowek, Congress Poland, Russian Empire. Along with his elder brother, Agaton Giller, Stefan Giller played an active role in the Polish independence movement and the Greater Poland Uprising.