For relatives who had middle names, try and determine (if possible) where the middle name originated. It could be a maiden name of the person’s mother or grandmother. A middle name could be the first or last name of a contemporary well-known person (nationally or locally) such as a politician, minister, etc. That middle name could have come from a neighbor, family friend, godparent, etc.
Or that middle name could simply be one that the parent liked for no other reason than that.