Mother and daughter are crazy (3)
I believe the answer is:
mad
'crazy' is the definition.
(I know that crazy can be written as mad)
'mother and daughter' is the wordplay.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'and' says to put letters next to each other.
'daughter' becomes 'd' (genealogical abbreviation).
'ma'+'d'='MAD'
'are' acts as a link.
(Other definitions for mad that I've seen before include "Extremely foolish" , "Berserk" , "Crazed" , "Crazy" , "Insane - furious" .)