Walks on south with relatives by marriage (8)

I believe the answer is:

stepsons

I'm a little stuck... Click here to teach me more about this clue!

'walks' is the definition.
Although both the answer and definition are plural nouns, I can't see how they can define each other.

'on south with relatives by marriage' is the wordplay.
'south' becomes 's' (synonyms).
'with' means one lot of letters go next to another.
'relatives by marriage' becomes 'steps' (I can't explain this - if you can you should believe this answer much more).
'on'+'s'='ons'
'ons' after 'steps' is 'STEPSONS'.

Can you help me to learn more?

I've seen this clue in The Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.