Complex sentence: Jessie Royce Landis plays Cary Grant's potential mother-in-law and in "North by Northwest" his mother although she was only seven years his senior and listed in her studio biography as 10 months younger.
Split into simpler sentences: Jessie Royce Landis plays Cary Grant's potential mother-in-law. She was only seven years his senior and was listed in her studio biography at 10 months younger.