Ambrose and two of his brothers, Robert and Christopher, were educated by Jesuits at Saint-Omer, then in Flanders.[nb 2] Both brothers became priests (Ambrose's elder brother, Henry, became a Franciscan),[6] and his half-sisters Dorothea and Susanna became nuns.[3] Ambrose married into the Tyrwhitts, a prominent family of Catholics from Kettleby in Lincolnshire, and with his wife Elizabeth (cousin to Robert Keyes)[7] had at least two sons, Robert and Henry. According to the Jesuit Oswald Tesimond, Rookwood was "well-built and handsome, if somewhat short",[1][8] which he compensated for by his taste in extravagant clothing. In author Antonia Fraser's opinion, this affectation was somewhat inappropriate at a time when "clothes were supposed to denote rank rather than money".[9] On his father's death in 1600, Rookwood inherited Coldham Hall, which subsequently became a refuge for priests.[3] The following year he joined the Earl of Essex's abortive rebellion against the government, for which he was captured and held at Newgate Prison.[10]