Complex sentence: Assuming she is elderly and ill, they take the apartment, but their hopes are quickly dashed when they realize that Mrs. Connelly is an energetic senior who enjoys watching her television at top volume day in and day out and rehearsing in a brass band.
Split into simpler sentences: Assuming she is elderly and ill, they take the apartment. However, they soon realize that Mrs. Connelly is in fact an energetic senior who enjoys watching her television at top volume day in and day out and rehearsing in a brass band.