How does Edmund and Goneril show madness in King Lear?

Edmund is a manipulative schemer and Goneril is both clever and evil. I don't see either one of these characters as displaying madness. The are self-absorbed and without conscience...... but I do not see them as crazy, just wicked. 

Both Edmund and Goneril serve as "foils," or characters that directly or indirectly reflect King Lear's gradual descension into madness. 

As both King Lear and Gloucester blindly see unequivocal love as the backbone of their sanity, their children's treachery and deceit picks away mercilessly at their hearts and sense of direction. Because Gloucester's story serves as a touchstone for Lear's tagic end, Gloucester's ultimate demise—catalyzed by the realization of Edmund's duplicity—underscores Lear's mental deterioration. Overwhelmed by jealousy of his legitimate brother, Edgar, and even believing that he—conceived by passion rather than by the dull apathy of wedlock—is the rightful heir, Edmund schemes and manipulates both his brother and his father, ultimately seeing success in his ploys: He strategically manufacures a letter from Edgar revealing Edgar's alleged motivations to kill his father, and solidifies this assertion by cutting himself so that it appears he heroically fights Edgar in protesst of Edgar's infedelity. A semblance of Edmund's conscience finally surfaces at the end of the play, however, when he declares that he is touched by Edgar's suffering as a beggar, and reveals his final machination to assasinate the King and Cordelia. His confession is too late, however, and through his murder of Cordelia, the King is stricken with irreversible grief and the burden of his "unfinished business"—he still feels that he is unable to achieve redemption, as he has not adequately expressed his compunction and contrition to Cordelia. Through Edgar's guile and deceit he manipulates the emotions of both King Lear and his fragile father—who, upon the realization of his mistake of disowning Edgar, attempts suicide. 

Reflecting Edmund's duplicity, Goneril's obsequious proclamations of love inflict irreversible physchological damage upon King Lear once he discovers that they are only an attempt to satiate her veracious hunger for power. Both Goneril and Regan's feigned love not only leave the King confused, lost, and enfeebled, but their deceit also leads the King to the realization of his mistake—disowning Cordelia in the tempest of his rage. Because he maintains stasis and sanity through the love of others, upon the death of his dearest daughter, Cordelia, he retreats back into his weak mental exasperation—insanity.

Despite the tragic ending of Lear, Gloucester's parallel situation highlights Lear as a martyr, eliciting catharsis from the audience; both Gloucester and Lear's foibles—Lear's blind rage and at times, frustrating insanity, and Gloucester's histrionic self-pity and weakness—are anulled. Ultimately, though Lear descends back into his mentally unstable, childlike state, his tragedy reveals the sanctity of a familial bond, which overpowers corporeal limitations and outlives death. 

-Alex Brunstad