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The relationship between Oliver & Orlando is highly co-incidental to that of the Dukes.
Oliver and Orlando are the sons of Sir Rowland De Boys. Both have a blood relationship but desire nothing but the blood of each other. The are bitter enemies, be it in monetary or social terms. Similarly, the Dukes also have a strong hatred towards each other. Even here, monetary terms(estate and kingdom) comes into play.
A very interesting thing is felt at the end. Both the villains - Oliver and Duke Fredrick, renunciate public and courtly life and prefer to live in the forest, ceding all their property to their brothers.
The nobility between Orlando and Duke Senior is also similar although the Duke has a feeling of pride in him.
These are the basic points ..... Hope it helps !!!