Marae and the people of the marae hold a wealth of information about their whanau. It is at the marae that you can find out the iwi, hapu, history and where the urupa (cemeteries) are.
There is also a high possibility that the people you talk to on the marae are also related to you, as most marae that are not urban are made up of whanau from the area, associated by blood.
Many Marae have produced Centennial Booklets and Marae Histories. The Marae could also have on display photographs of many of the people who are from there. The photos may not be labeled so ask around as people will be able to tell you who they are.
It is appropriate for you to visit in person and not make a phone call. Be prepared to spend a bit of time, and not try to fit your visit into a 1 hour appointment.