Who is Tomas and Jesusa from Lilith's Brood and what is their importance?

Tomas and Jesusa, who are siblings, are members of the Human village that has been hiding on Earth. Their village managed to find a fertile Human long ago and there is now a group of people in the village that can have children. The gene pool has been interbred for so long that all the people there have debilitating diseases. Tomas and Jesusa are wandering in the wilderness one last time before they have to start breeding for their village when they meet Jodahs. Tomas and Jesusa have heard all their lives that the Oankali are the devil but they have been living so long with sickness and watching young babies and deformed children die, that when Jodahs heals them they seem rather willing to agree to stay with Jodahs. Tomas and Jesusa agree to take Aaor, Jodahs's sibling, to their village in the hopes that Aaor can find Human mates as well.