Disastrous couple keeping son in poor state (9)
I believe the answer is:
disrepair
'poor state' is the definition.
(I've seen this before)
'disastrous couple keeping son' is the wordplay.
'disastrous' becomes 'dire' (I've seen this in another clue).
'couple' becomes 'pair' (synonyms).
'keeping' indicates putting letters inside.
'son' becomes 's' (genealogical abbreviation for son).
'dire'+'pair'='direpair'
'direpair' going around 's' is 'DISREPAIR'.
'in' is the link.
(Other definitions for disrepair that I've seen before include "broken-down state" , "Neglected condition" , "Poor working order" , "In need of mending" , "rack and ruin" .)