GREP InDesign re-arranging multiple names

Already embedded within InDesign is a script (Scripts > Application > Samples > JavaScript > SortParagraphs.jsx which will sort alphabetically. That is half your battle, anyway.

A GREP might be: ^(.+)\s(.+) and change to $2 $1. It would leave behind the awkward name patterns that you might clean up manually.

Replying late to this as I just saw it, but if most of the names in your list are single firstname, single lastname, it probably wouldn't be too hard to find the outliers and manually join them where you don't want them to break, do the transposition using GREP and then replace the join characters with spaces. Here's what I mean: 

Butcher Thomas

de#Boag Michael

Holland-Kemp Kelly

Pitt Avery#Mae-Anne

Smith John#Peter

Find Grep: (.+) (.+)

Change Grep: $2 $1

Then find-change # to space. 

There would be no way. You'd need a pattern.

Thomas

Micheal

Mae-Anne

John Peter

All have different patterns

Partnered with double barrel surnames, surnames singular.

There's no way to distinguish

Holland-Kemp Kelly

Pitt Avery Mae-Anne

Smith John Peter

The pattern is too diverse.