I don’t know the answer to most of your questions but the name change would have been easy according to Delta’s website. Dad said he bought the older kid a ticket not that he changed the older kids flight but no proof that I have read.
Guidelines for Name Correction for Domestic & International Tickets
Correction to the First or Middle Name
Travel agents may make a correction to the first or middle name and reissue the ticket without a waiver code providing the following conditions are met:
All flights on the ticket must be Delta–operated (including Delta Connection carriers ). If the ticket includes flights operated by any other carrier, please contact Delta Sales Support for assistance.
Only one reissue for a name correction is allowed per passenger ticket. If the name requires further correction and the ticket needs to be reissued a second time, please contact Delta Sales Support for assistance.
That is a name correction. It is for fixing the name of the ticketed passenger. I have had problems with the suffix of name. I have it added when it’ is not listed correctly. This is definetly not for changing the ticketed person.