I would like to invite my graduate(Electronics Engineering) sister and my parents to visit U.S. Now, my sister may/may not come to U.S to study M.S depending on her marriage situation. I know there is a class of visa for intending students. I would like my sister to visit universities in the U.S, meet professors and take GRE exams if she wants to. What are the requirements to be met to obtain this type of visa and what is this visa called? What are the chances of getting this visa for a single, graduate, 22 year old lady? Also, what are the chances of my parents travelling along with her on a tourist visa to visit us and tour U.S? Thanks and appreciate the help.