One is not expected to live on them (4,4)
I believe the answer is:
last legs
'one is not expected' is the definition.
I can't judge whether this definition defines the answer.
'live on them' is the wordplay.
'live' becomes 'last' (synonyms).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'them' becomes 'legs' (I can't justify this - if you can you should give a lot more credence to this answer).
'last'+'legs'='LAST LEGS'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for last legs that I've seen before include "Final Limbs denoting ebbing strength" , "Final dregs of energy - of lower limbs?" , "Things are bad when you are on these!" .)