It's established that they will be taken in (8)
I believe the answer is:
accepted
This clue could be a double definition.
'it's established that they' is the first definition.
'accepted' can be an answer for 'it's established' (I've seen this before). I am unsure of the rest of the definition.
'taken in' is the second definition.
'accepted' can be an answer for 'taken' (accepting is a kind of taking). I am not sure about the 'in' bit.
'will be' acts as a link.
Can you help me to learn more?
(Other definitions for accepted that I've seen before include "Tolerated; believed to be correct" , "Received; approved" , "Conventional -- customary" , "Welcomed" , "such behaviour normal?" .)