Complex sentence: Jacob himself always spelled his name with an "i", while his cousin, Salomon's son Jacob Salomonszoon van Ruysdael, also a landscape artist, spelled his name with a "y".
Split into simpler sentences: Jacob himself always spelled his name with an "i". His cousin, Salomon's son Jacob Salomonszoon van Ruysdael, also a landscape artist, spelled his name with a "y".