Only The Testor Trips the GFCI
Many times people think they have GFCI outlets wired correctly and they are not. If the Outlet is tripped and the additional outlets are live the additional outlets were not wired on the load side. This has been the case for almost all the mis wired GFCI's I have been called in to repair. If a GFCI fails it usually will not power the down stream devices. With 2 devices not working I would verify the "line" and "load" connections.