Eric Swalwell. Hello?
Found Oswald's military records including discharge and courts martial. He had a brother serving in the Air Force in Japan (didn't know that). Lots more of interest in there.
180-10072-10186 .pdf
That file indicates that he had two brothers: one a married civilian and the other serving in the Air Force. Oswald wanted out of the Marines to take care of his mother because his brothers couldn't.