What is the name of this christian group?

It is a brother and sister who sing christian songs, and on every album they always have a song with African chanting in it. Their grandfather was an atheist for a long time, until a friend dragged him to a christian revival. He ended up marrying the friend, and he became a very devout christian. After he was married he decided to sell all of his earthly possessions and go to Africa as a missionary. If anyone knows the name of the brother and sister group, please tell me. Thank you so very much.