Before ruler, fathers and sons have to meet the standard (4,6)
I believe the answer is:
pass muster
'to meet the standard' is the definition.
(to pass muster is to meet certain criteria)
'before ruler fathers and sons' is the wordplay.
'before' means one lot of letters go next to another.
'ruler' becomes 'muster' (I can't explain this - if you can you should give a lot more credence to this answer).
'fathers' becomes 'pas' (pa is a kind of father).
'and' says to put letters next to each other.
'sons' becomes 's'.
'pas'+'s'='pass'
'muster' put after 'pass' is 'PASS MUSTER'.
'have' acts as a link.
(Other definitions for pass muster that I've seen before include "To fit the bill" , "Be good enough" , "Satisfy, suffice" , "appear acceptable" .)