Modular branch vessel stent-graft assemblies for the treatment arterial or vascular disease at the branch of two or more arteries or blood flow passageways, including, for example, abdominal aortic aneurysms are assembled in a patient's trunk/parent artery, from at least two components; a first component and a second component. The first and second components each include a first and second window, or fenestration. The second component couples with the first component by fitting at least partially in the first component to form the modular branch vessel stent-graft assembly with two selectively locatable branch openings. As the first and second components are deployed, the second component is selectively position able relative to first component so that the first and second component first and second windows overlap to form two branch openings whose longitudinal and angular positions are selectable within a range.