Family shows concern describing Miller's last play (5,8)
I believe the answer is:
blood-brothers
'play' is the definition.
(I've seen this before)
'family shows concern describing miller's last' is the wordplay.
'family' becomes 'blood' (blood can mean one's family).
'shows concern' becomes 'bothers' (to bother with something is to show concern for it).
'describing' means one lot of letters goes inside another (describe can mean to form the outline of).
'last' says to take the final letters.
The final letter of 'miller' is 'r'.
'bothers' going around 'r' is 'brothers'.
'blood'+'brothers'='BLOOD-BROTHERS'
(Another definition for blood-brothers that I've seen is " Men sworn to treat each other like relatives".)