Incesttuous

a.	1.	Guilty of incest; involving, or pertaining to, incest; as, an incestuous person or connection. Ere you reach to this incestuous love, You must divine and human rights remove. - Dryden.
	2.	resembling incest; between people or groups so closely related as to make such activity improper or unethical; as, an incestuous coziness between the management of the company and its union; an incestuous relationship between the salesman and the purchasing manager.