The Agathocles lands in Africa card is the only way for the Greeks to land in Africa in the 4-player game.
But why would they? They are not allowed to enter Carthage, so what's the point of taking Kerkouane only? Sorry if I must be missing something obvious here.
Section 17.2.1 First bullet. Treat Kerkouane as a normal port for the Greeks as long as Greek CU are present in the space. So if Agathocles does land in Africa, the Greeks can reinforce the space and if they are victorious in battle in the Carthgo space knock Carthage out of the war.