With eight members the Spanish set firm up (7)
I believe the answer is:
octuple
'with eight members the spanish set firm up' is the definition.
I can't tell whether this defines the answer.
'the spanish set firm up' is the wordplay.
'the spanish' becomes 'el' ('the' in Spanish).
'set' becomes 'put' (synonyms).
'firm' becomes 'co' (a firm is a company).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'el'+'put'+'co'='elputco'
'elputco' written backwards gives 'OCTUPLE'.
Can you help me to learn more?
(Other definitions for octuple that I've seen before include "Eightfold" , "multiply by eight" , "Couplet (anag)" , "more than seven times" , "8 times" .)