Thought of jointly as being indecisive (2,3,5)
I believe the answer is:
in two minds
'thought of jointly' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'as being indecisive' is the wordplay.
'as' becomes 'in' (I've seen this in other clues).
'being indecisive' becomes 'twominds' (I can't explain this - if you can you should give a lot more credence to this answer).
'in'+'twominds'='IN TWO MINDS'
Can you help me to learn more?
(Other definitions for in two minds that I've seen before include "Torn" , "where similar ideas may be foolish or clever" , "Wavering, undecided" , "The outcome is uncertain" , "like Dr Jekyll at times?" .)