Lets go through some of those points
They married in not the nearest register office – to marry in a register office they have to give 21 days notice the notice would need to be given in their home parish and that of the register office usually it would be the closest as you say – maybe they didn’t marry in the closet ones as people thought they were already married, maybe one party was very ill and they had to get married so the other could inherit
Anyway maybe they gave a false address that would enable them to be married in the register office without notice being have to given at the register office nearest to their home.
(I know this is a lot of maybes) the question we really need to answer is who was actually living at the address they gave when they got married .
Maybe they were embarrassed about getting married in a register office and not a church so they didn’t say anything to the rest of the family just let them believe it was a church ditto the date not being when they met before they had children.
My great gran got married when she was 8 months pregnant (with her first child) in a register office (they were Methodists) a marriage had to be according to the rites of Church of England unless they were Jewish or Quakers so perhaps they were not of Christian faith?
Perhaps she was illegitimate that would explain the made up father
The 2 different maiden names would usually indicated that she was illegitimate or that she had been married before.
The witnesses are not always family members were they clerks or friends or just random people of the street perhaps these were the owners of the address they gave
Finally if the groom was in the army he would have to gain permission form his officers in order to marry this was because the army would have to support the wife if the groom died and so quite a lot of the time permission was NOT granted.
Toni