Complex sentence: Most members joined the Association of Artists in Revolutionary Russia (AKhRR), whose members leaned on the traditions of Peredvizhniki and aspired to create works of art understandable by people and faithfully reflecting the Soviet validity.
Split into simpler sentences: Most members joined the Association of Artists in Revolutionary Russia (AKhRR). Its members built on the traditions of Peredvizhniki and aspired to create works of art accessible to the common people and that faithfully reflecting the Soviet validity.