Complex sentence: The staffage of his works has at times been attributed to other painters, such as Anthonie Palamedesz and Dirck Hals, but these attributions are doubted as van Delen lived in relative isolation and it would not have been easy for him to collaborate with these artists.
Split into simpler sentences: The staffage of his works has at times been attributed to other painters, such as Anthonie Palamedesz and Dirck Hals. There is some doubt about these attributions as van Delen lived in relative isolation and it would not have been easy for him to collaborate with these artists.