One visiting fat son with joint landowner’s position (9)
I believe the answer is:
lairdship
'landowner's position' is the definition.
(a laird is a Scottish landowner)
'one visiting fat son with joint' is the wordplay.
'one' becomes 'i' (Roman numeral).
'visiting' indicates putting letters inside.
'fat' becomes 'lard' (lard is a kind of fat).
'son' becomes 's' (genealogical abbreviation for son).
'with joint' becomes 'hip' (part of body. I am not sure about the 'with' bit.).
'i' placed into 'lard' is 'laird'.
'laird'+'s'+'hip'='LAIRDSHIP'
(Another definition for lairdship that I've seen is " position up north".)