Mambo, an old man suffers from mental illness and poor eyesight .He has two sons, Jeff and Jack who he orally told would inherit his property. However, his mistress Chantal, wrote a will on his behalf and convinced him to append his Thumbprint to it. The will transfers all of Mambo`s property to Chantal upon his death. Mambo has died and his sons have discovered about Chantal`s deception and are aggrieved.

(i) Discuss the legal principles applicable