Complex sentence: Leone was convinced that Jolly Film were withholding his share of the profits and sued them and joined forces with producer Alberto Grimaldi who founded the Produzioni Europee Associate (PEA) film company.
Split into simpler sentences: Leone was convinced that Jolly Film were withholding his share of the profits. He sued them and joined forces with producer Alberto Grimaldi, who founded the Produzioni Europee Associate (PEA) film company.