If you want to deal with multi-value fields then you have to merge them first to a single field.
There is an action for that.
https://docs.mp3tag.de/actions/merge-duplicate-fields
In this action, set a separator that is different from the \\ as this is treated as field separator and you are back to square one.
As for the illogical names which sometimes have a forename and a surname and sometimes are just as they are .... you probably have to find some kind of semantic filter to deal with them, e.g. no name with Orchestra or Philharmonic is treated ...
Actually, there have been a couple of discussions on whether one should swap name parts or not.
e.g.
How to rearrange artist name
In short: don't