Three daughters -- two blocking stubborn ass, third daughter at sea (7)
I believe the answer is:
muddled
'at sea' is the definition.
(at sea can mean confused or uncertain)
'three daughters two blocking' is the wordplay.
'three daughters' can mean three substitutions for 'daughters'.
'daughters' becomes 'mule' (I can't explain this - if you can you should believe this answer much more).
'daughters' becomes 'd'.
'daughters' becomes 'd'.
'two' says to double the letters.
'blocking' means one lot of letters goes inside another.
'd' duplicated is 'dd'.
'mule'+'d'='muled'
'muled' placed around 'dd' is 'MUDDLED'.
'stubborn ass third daughter' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for muddled that I've seen before include "Confused, all mixed up" , "Disordered, confused" .)