The combined sentence uses a compound subject.
Explanation
The subject of a sentence is said to be the protagonist.
It maybe a person, place, or idea. compound subject using sentences has multiple subjects (two or more) joined by 'and' or 'or'.
When using multiple subjects, the use of subject-verb agreement is important to express the proper idea of the sentence.
Here, Sir Edmund and Cecil are subjects.
As there are two subjects, this is a sentence that uses two subjects, hence it is a compound subject.