Who agreed to help Umbopa and on what condition?

The Witch Hunt is the title of Chapter Ten. After Umbopa reveals his true identity, Infadoos kneels before him recognizing him as Ignosi, his rightful ruler. Umbopa/Ignosi swears Infadoos to loyalty, and then asks the white men to help him with his overthrow of Twala. He offers the men diamonds, but Sir Henry rejects the offer in favor of assisting Ignosi simply because Twala deserves to be destroyed. Good also joins the revolution: his only stipulation is that he be allowed to wear trousers. Quatermain, however, proclaims his mercenary nature and accepts the diamonds as payment; he then insists they also find Sir Henry’s brother if at all possible.