Complex sentence: The president instead wants to expand his own influence by marrying Ferdinand to Lady Milford, the duke's mistress, but Ferdinand rebels against his father's plan and tries to persuade Luise to elope with him.
Split into simpler sentences: The president instead wants to expand his own influence by marrying off his son Ferdinand to Lady Milford, the duke's mistress. However, Ferdinand rebels against his father's plan and tries to persuade Luise to elope with him.