Who is Eustace and Claude from Life with Jeeves and what is their importance?

Eustace and Claude (twins) are Berties relatives. They are younger than Bertie, and we first meet tham at Twing Hall, where they are being tutored by Rev. Heppenstall. As the novel progresses, we learn that the twins have been expelled from Oxford University. Aunt Agatha then sends the boys to South Africa.